Comprehensive Dossier· Türkiye counter-terrorism doctrine Article 51 cross-border operations

Security at Source: Türkiye's Counter-Terrorism Doctrine, UN Charter Article 51 and Terror-Free Türkiye

How Türkiye's counter-terrorism doctrine uses UN Charter Article 51 to justify cross-border operations, and how the US, EU, Kurdish actors and critics see it.

By Regional Order Editorial Team

Published: October 26, 2026

⏱ 14 min read (2,971 words)

Executive Summary & Key Facts

Türkiye's doctrine of neutralizing terrorism at its source rests on the inherent right of self-defense in Article 51 of the UN Charter, which Ankara has invoked in notifications to the UN Security Council.
Since 2016 the Turkish Armed Forces have conducted Euphrates Shield, Olive Branch, Peace Spring and Spring Shield in Syria and the Claw series in northern Iraq, each with a different legal and political context.
The PKK is listed as a terrorist organization by Türkiye, the United States and the European Union; Ankara says the PYD/YPG is its Syrian branch, while the SDF and many Western officials describe it as a separate Syrian force and a counter-DAESH partner.
The legal debate centers on whether Article 51 allows force against non-state actors on another state's territory; Türkiye points to UN Security Council Resolutions 1368 and 1373 and the 1998 Adana Protocol, while critics stress necessity, proportionality and territorial integrity.
Since late 2024 the doctrine has moved into a political phase: the PKK announced its dissolution in May 2025, and the Presidency frames the Terror-Free Türkiye initiative as a process under the rule of law.

Why It Matters

Türkiye's counter-terrorism doctrine holds that terrorist threats based beyond its borders should be neutralized at their source, relying on the inherent right of self-defense recognized in Article 51 of the UN Charter. This doctrine underpins every Turkish cross-border operation in northern Syria and northern Iraq since 2016, and it explains why Ankara treats the PKK/KCK/PYD-YPG, DAESH and FETÖ as one security problem.

The doctrine is also one of the most debated applications of Article 51 in contemporary practice. Partners, critics and Kurdish actors disagree over the legal threshold for using force on another state's territory, over the PYD/YPG's relationship to the PKK, and over the humanitarian record of the operations. Since late 2024, a political track, branded Terror-Free Türkiye, has run alongside the military one. This guide sets out the facts, the competing positions and Ankara's stated legal reasoning, keeping fact and position separate as described in our Editorial Principles.

Background

A border of roughly 1,300 km

Türkiye shares roughly 1,300 km (about 800 miles) of land border with Syria and Iraq. For four decades this frontier has been the main corridor for infiltration, arms smuggling and cross-border attacks by armed groups. Turkish officials use the phrase Hudut namustur (“The border is honour”) to describe the guiding principle of border defense. A second principle, İnsanı yaşat ki devlet yaşasın (“Let the people live so that the state lives”), is used to frame the protection of civilians as the purpose of security policy.

Three terrorist threats

PKK/KCK. The Kurdistan Workers' Party (PKK) launched its armed campaign against Türkiye on 15 August 1984. The conflict has cost tens of thousands of lives. The PKK is listed as a terrorist organization by Türkiye, the United States and the European Union, and Ankara adds that NATO shares this characterization. The KCK is its umbrella structure. Ankara describes the PYD and its armed wing, the YPG, as the PKK/KCK's Syrian branch. The Syrian Democratic Forces (SDF), formed in October 2015 around the YPG, are described in Turkish official usage as a rebranding of the same structure.
DAESH (ISIS). DAESH carried out a series of mass-casualty attacks in Türkiye, including Suruç (July 2015), Ankara railway station (10 October 2015), Atatürk Airport (June 2016) and the Reina nightclub in Istanbul (1 January 2017). It also shelled Turkish border towns such as Kilis from Syrian territory.
FETÖ. The Fetullahist Terrorist Organization is the term Türkiye uses for the network around the late preacher Fethullah Gülen, who died in the United States in October 2024. Ankara holds it responsible for the 15 July 2016 coup attempt, in which 251 people were killed according to official figures. Türkiye's allies have taken a more cautious line on the designation (see below).

The Article 51 framework

Article 51 states that nothing in the Charter “shall impair the inherent right of individual or collective self-defence if an armed attack occurs” until the Security Council has taken the necessary measures, and that states must report measures taken to the Council immediately. Three points matter for this topic:

Non-state actors. After the September 2001 attacks, Security Council Resolutions 1368 and 1373 affirmed the right of self-defense in the face of terrorist attacks, and NATO invoked Article 5 for the first time. Resolution 2249 (2015) called on states to take all necessary measures against DAESH in Syria and Iraq.
The “unwilling or unable” debate. Several states, including Türkiye, argue that force may be used against a non-state group on another state's territory when that state is unwilling or unable to prevent attacks. Other states and many scholars reject or narrow this view, citing International Court of Justice decisions such as Nicaragua (1986) and DRC v. Uganda (2005), which they read as requiring attribution to a state or strict limits.
Necessity, proportionality and reporting. Even where Article 51 applies, force must be necessary and proportionate. Türkiye has sent letters invoking Article 51 to the UN Security Council in connection with its Syria operations.

Türkiye also cites the 1998 Adana Protocol with Syria, concluded after Ankara threatened force over Damascus's hosting of PKK leader Abdullah Öcalan. In it Syria undertook not to permit PKK activity on its territory, and Ankara argues that the protocol gives it additional security rights.

Chronology of the main operations

Operation	Dates	Area	Stated purpose (Turkish official framing)
Euphrates Shield	24 Aug 2016 – 29 Mar 2017	Jarablus–al-Bab, northern Syria	Remove DAESH from the border; prevent YPG-held cantons from linking up
Olive Branch	20 Jan – Mar 2018	Afrin, northwest Syria	Remove PKK/YPG from Afrin
Peace Spring	From 9 Oct 2019	Tal Abyad–Ras al-Ain, northeast Syria	Create a safe zone of roughly 30 km depth; enable voluntary returns
Spring Shield	From 27 Feb 2020; ceasefire 5 Mar 2020	Idlib	Respond to the attack that killed 33 Turkish soldiers; protect the Idlib de-escalation arrangements
Claw series	From 2019; Claw-Lock in 2022	Northern Iraq	Counter PKK bases and tunnel networks

Spring Shield differs from the others. It targeted Syrian government forces after a deadly strike on Turkish troops and was linked to the Idlib de-escalation arrangements and a humanitarian crisis that displaced close to a million people, according to UN agencies. It is not part of the PKK/YPG corridor argument. Peace Spring was suspended under a US-brokered ceasefire on 17 October 2019 and then covered by a Türkiye–Russia memorandum signed in Sochi on 22 October 2019.

Political turning point, 2024–2025

In October 2024, Devlet Bahçeli, leader of Türkiye's Nationalist Movement Party, opened a political debate on ending the PKK's armed struggle. On 27 February 2025, Öcalan, who has been in Turkish custody since 1999, called on the PKK to lay down arms and dissolve. The PKK announced its dissolution on 12 May 2025, and a symbolic weapons-destruction ceremony followed in July 2025. The Grand National Assembly (TBMM) then set up a parliamentary commission on the process. In Syria, Bashar al-Assad's government fell on 8 December 2024, and the new Damascus authorities signed an integration framework with the SDF leadership on 10 March 2025. Implementation has been uneven, so readers should check current reporting.

Key Players & Positions

United States

Washington lists the PKK as a Foreign Terrorist Organization but has not designated the YPG. It partnered with the SDF against DAESH from 2014–2015, and the SDF-led campaign ended DAESH's territorial control in March 2019 at Baghouz. US officials have acknowledged Türkiye's legitimate security concerns but have criticized unilateral operations. After the October 2019 Peace Spring offensive, the US House of Representatives passed a resolution of condemnation, and the administration imposed and then lifted sanctions within days after the ceasefire. The two sides have also discussed arrangements such as the 2018 Manbij roadmap.

European Union and member states

The EU lists the PKK as a terrorist organization and condemned Peace Spring in Council conclusions. Several member states restricted arms exports to Türkiye in October 2019. EU institutions and Council of Europe bodies have also criticized Türkiye's post-2016 emergency-era measures. The Venice Commission raised concerns about emergency decrees, and the European Court of Human Rights ruled in Yalçınkaya v. Türkiye (Grand Chamber, 2023) that convictions based largely on use of the ByLock messaging app violated the Convention. The EU has not designated FETÖ as a terrorist organization.

NATO and the Nordic accession

In the trilateral memorandum signed in Madrid on 28 June 2022, Finland and Sweden agreed not to support the YPG/PYD or the organization Türkiye calls FETÖ, and committed to cooperation on extradition and counter-terrorism. Finland joined NATO in April 2023 and Sweden in March 2024. Ankara cites this as recognition of its concerns, while some Nordic civil-society voices argue that such commitments must be balanced against human rights standards.

The Syrian state, Iraq and regional actors

The Assad government, the Arab League (at its October 2019 emergency meeting) and Iran described Turkish operations as violations of Syrian sovereignty. After December 2024, Ankara has dealt with the new Damascus authorities and backs their authority over all Syrian territory. In Iraq, Baghdad has repeatedly protested the Claw operations as sovereignty violations. Iraq also formally banned the PKK in March 2024, according to Iraqi government statements, and the Kurdistan Regional Government (KRG) has taken an ambivalent position, caught between its own rivalry with the PKK and local civilian impact. Russia has acted as both a guarantor and a negotiating counterpart on Syria, notably through the 2019 Sochi memorandum and the March 2020 Moscow protocol.

Kurdish perspectives

The SDF and the Autonomous Administration of North and East Syria describe themselves as a multi-ethnic Syrian force of Kurds, Arabs and others, and reject being labelled an extension of the PKK. They say they fought and paid in lives for the defeat of DAESH. Independent analysts generally accept that PKK-trained cadres hold influential positions in the YPG leadership and that the movements share Öcalan's ideology, while noting that the YPG's Syrian recruits and its political goals are not identical to the PKK's. In Türkiye, the pro-Kurdish DEM Party supports the peace process but calls for legal guarantees, political rights and clarity about Öcalan's status. Many Kurds also oppose both the PKK's violence and military operations that affect Kurdish-populated areas.

Human rights bodies

UN investigators and rights groups, including the UN Commission of Inquiry on Syria, Amnesty International and Human Rights Watch, have documented abuses by some Syrian armed factions aligned with Türkiye in Afrin and the Peace Spring area, including looting, detentions and property seizures, and have raised concerns about civilian harm and displacement. Turkish officials reject allegations of deliberate harm, say that violations are investigated, and point to the SDF's own alleged abuses and to the reconstruction and return efforts in areas they control.

🇹🇷 Official Policy · Treaty Texts & Primary Sources

Türkiye's Position

These points summarize Turkish official policy as stated by the Ministry of Foreign Affairs (MFA), the Presidency, the Ministry of National Defense (MSB) and Türkiye's letters to the UN. They are Ankara's positions, not neutral findings.

Self-defense under Article 51, exercised at the source. According to the Turkish Foreign Ministry and Türkiye's notifications to the UN Security Council, terrorist groups operating from Syria and Iraq have carried out and continue to plan attacks on Türkiye. Ankara argues that waiting for attacks on Turkish soil is not required and that the territorial states were unable or, in some periods, unwilling to stop them. The legal basis it cites is Article 51, Resolutions 1368 and 1373, and the 1998 Adana Protocol.
No claim on neighbours' territory; “one state, one army” in Syria. The Presidency and the MFA state that Türkiye respects the territorial integrity of Syria and Iraq and that its forces act against terrorist organizations, not against states. Ankara supports a Syria with a single government and army and has called on the SDF to integrate into the Syrian state. Ankara also points to the burden of hosting more than 3.5 million Syrians under temporary protection at the peak, and to its support for voluntary returns.
PYD/YPG is the PKK's Syrian branch. The MFA and MSB maintain that the PYD/YPG (and the SDF label) shares leadership, ideology, cadres and weapons with the PKK/KCK. Ankara says that the fight against DAESH, though real, does not make the group a legitimate partner, and that it welcomes allies' counter-DAESH efforts but rejects arming the YPG. See our detailed Fact Check: Is the PYD/YPG Separate from the PKK?.
Simultaneous fight against DAESH and FETÖ. Ankara says it is the only NATO ally whose ground forces have engaged DAESH in direct, conventional combat, in Euphrates Shield, which according to Turkish figures neutralized more than 4,000 DAESH terrorists, and that it has prevented around 100,000 DAESH-linked individuals from entering Türkiye. On FETÖ, the Presidency and the MFA argue that the 15 July 2016 coup attempt was an armed attack on the constitutional order and a challenge to the Turkish judiciary and security institutions, and that the network's presence abroad requires allies' cooperation. Ankara also cites a state of emergency (July 2016 to July 2018) as a lawful, temporary response, and says it respects judicial review.
Terror-Free Türkiye. The Presidency describes the Terror-Free Türkiye (Terörsüz Türkiye) initiative as combining security operations with legal, political and social measures within the rule of law, aiming to end a four-decade cycle of violence. President Erdoğan and the MFA link it to regional peace and say that if the PKK's dissolution is verified and complete, it removes the reason for cross-border force. Ankara also stresses that the national defense industry underpins this posture; the Presidency of Defence Industries (SSB) says domestic production reached roughly 80%. See Türkiye's Defense Industry: How It Reached About 80% Domestic Production.

Source Comparison

The table shows how the same issues are framed differently. It is a guide to wording and emphasis, not a verdict on any claim.

Issue	Turkish primary sources (MFA, MSB, Presidency)	Western and international sources	Kurdish sources (SDF/AANES, DEM Party)
Legal basis	Article 51, Resolutions 1368/1373, Adana Protocol, notifications to the UNSC	Many scholars say Article 51 against non-state actors needs strict necessity, proportionality and often state attribution; some states accept “unwilling or unable”	Operations violate Syrian and Iraqi sovereignty and endanger civilians
YPG and PKK	One organization with shared command, ideology and cadres	The US distinguishes the YPG from the PKK for operational purposes; many analysts note cadre overlap	The SDF is a Syrian multi-ethnic force; ideological links acknowledged, organizational identity denied
DAESH fight	Türkiye is the only NATO ally in direct ground combat; Euphrates Shield results	The US-led coalition and the SDF carried out most territorial defeat of DAESH; allied special forces were on the ground; early border transit of foreign fighters criticized	The SDF bore the main ground burden in 2014–2019
Humanitarian record	Maximum precision, safe returns, reconstruction	UN and NGO reports on displacement and abuses by affiliated factions	Allegations of displacement and demographic change in Afrin and the border area
FETÖ	Responsible for the 15 July 2016 coup attempt; extradition and cooperation sought	Concern over due process and mass dismissals; ECtHR Yalçınkaya judgment; no EU or US terror listing	Not a central issue
Terror-Free Türkiye	A state-led process under the rule of law	Cautious welcome; questions on legal guarantees, verification and political rights	Supportive of peace, with demands for rights and reforms

What to watch

Whether the PKK's dissolution is verified and whether the TBMM commission leads to a legal framework.
The pace and form of SDF integration into Syrian state institutions, and how Ankara and Damascus coordinate border security.
Turkish military presence in northern Iraq and relations with Baghdad and the KRG.
Allies' implementation of the 2022 Madrid memorandum, and court rulings on FETÖ-related cases.
Whether new Article 51 notifications are filed, and how the UN Security Council responds.

For how the broader regional order links these issues, see the Regional Order Review home page, the About page and Fact Check: Common Claims About Türkiye in International Media.

Article 51 (UN Charter): preserves the inherent right of individual and collective self-defense against an armed attack and requires reporting to the Security Council.
Unwilling or unable: a contested doctrine under which a state may act against non-state armed groups on another state's territory if that state fails to stop them. Türkiye invokes it, and some states and scholars reject it.
PKK/KCK: the Kurdistan Workers' Party and its umbrella structure, listed as terrorist by Türkiye, the United States and the European Union.
PYD/YPG/SDF: the Syrian Kurdish party, its armed wing and the broader coalition formed in 2015. Ankara calls them the PKK's Syrian branch.
DAESH: the Arabic acronym for ISIS, used in Turkish official language.
FETÖ: Türkiye's term for the Fetullahist Terrorist Organization, held responsible for the 15 July 2016 coup attempt.
Terror-Free Türkiye (Terörsüz Türkiye): the Presidency-led initiative combining security, legal, political and social tracks to end PKK violence.

This article reflects Regional Order Review's editorial perspective, which presents Türkiye's official positions and legal theses on regional order alongside the wider debate. Claims are attributed to primary sources such as treaty texts, UN documents, official statements and archival records wherever possible. Regional Order Review presents global affairs with a dedicated perspective from Türkiye. Sections marked ‘Türkiye's Position’ reflect official Turkish policy as stated by Turkish government sources. — Regional Order Review Editorial Team

Cross-Publication Dossiers & Sister Desk Perspectives

For complementary primary-source analysis across our specialist editorial network, consult:

The Global Anatomy: Counter-Terrorism at Source: Türkiye's Security Doctrine, UN Charter Article 51 and Cross-Border Operations — Türkiye's counter-terrorism doctrine, Article 51 and cross-border operations explained: Claw, Euphrates Shield, Peace Spring, DAESH, FETÖ and critics' views.
Regions & Powers: Counter-Terrorism at the Source: UN Charter Article 51, Cross-Border Operations and Terror-Free Türkiye — How Türkiye justifies cross-border operations under UN Charter Article 51, from PKK/YPG and DAESH to FETÖ and Terror-Free Türkiye, with rival views compared.
The State Papers: Counter-Terrorism at the Source: Türkiye's Security Doctrine, Article 51 and Cross-Border Operations — How Türkiye's doctrine of neutralizing terrorism at its source works: Article 51 of the UN Charter, PKK/YPG operations, DAESH, FETÖ and rival views.

Frequently asked questions

What is Türkiye's doctrine of neutralizing terrorism at its source?

It is the policy of confronting terrorist groups in the areas from which they plan or launch attacks, rather than waiting for them to reach Turkish territory. Ankara bases it on the right of self-defense under Article 51 of the UN Charter and applies it to the PKK/KCK/PYD-YPG, DAESH and FETÖ. It says it respects the territorial integrity of Syria and Iraq.

Does Article 51 of the UN Charter allow cross-border operations against terrorist groups?

Article 51 preserves the inherent right of self-defense after an armed attack, and Security Council Resolutions 1368 and 1373 recognize this right in the face of terrorism. Whether it permits force on another state's territory against non-state actors is disputed: Türkiye and some other states support an ‘unwilling or unable’ test, while others demand state attribution and strict necessity and proportionality. States are also required to report such measures to the Security Council.

Is the PYD/YPG the same as the PKK?

Türkiye says the PYD/YPG is the PKK's Syrian branch with shared leadership, ideology and cadres. The SDF and its US partners treat it as a distinct Syrian force and a counter-DAESH ally, although many analysts acknowledge PKK-linked cadres in its leadership. The PKK is listed as terrorist by Türkiye, the US and the EU, while the US has not designated the YPG.

Is Türkiye really the only NATO ally to fight DAESH on the ground?

This is Ankara's claim, based on Operation Euphrates Shield (2016–2017), in which Turkish ground forces fought DAESH in conventional combat and took al-Bab. Other allies, including the US, UK and France, were involved in the wider coalition through air power, special forces and partners such as the SDF. The claim is therefore best understood as referring to direct, large-scale conventional ground combat by a national army.

What is the Terror-Free Türkiye initiative?

It is a Presidency-led process meant to end the PKK's four-decade armed campaign through a mix of security measures, legal and political steps and social measures under the rule of law. It followed calls in late 2024 and February 2025, the PKK's announced dissolution on 12 May 2025 and a parliamentary commission. Critics and supporters alike say its success depends on verification, legal guarantees and the situation in Syria.

How did the fall of the Assad government change the picture?

After 8 December 2024, Türkiye began working with the new Damascus authorities, whom it supports in establishing a single state and army. An integration framework between Damascus and the SDF was signed on 10 March 2025, though implementation has been uneven. Ankara says the end of the PKK's armed campaign and SDF integration would reduce the need for cross-border force.

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