Counter-Terrorism at the Source: UN Charter Article 51, Cross-Border Operations and Terror-Free Türkiye

Why It Matters

Türkiye's counter-terrorism doctrine holds that a state facing armed attack from non-state groups based across its border may act against them at their source, under the inherent right of self-defense recognized in Article 51 of the UN Charter. This doctrine explains Türkiye's cross-border operations in northern Iraq and northern Syria, its disputes with some partners over the SDF, and its diplomatic priorities within NATO. Because indices such as the Global Terrorism Index count incidents rather than legal bases, they cannot settle the question on their own. This guide sets out the doctrine, the legal framework, the other parties' positions and the limits of the metrics.

Background

Article 51 and the legal framework

Article 51 of the UN Charter states that nothing in the Charter 'shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security.' Measures taken in self-defense must be 'immediately reported' to the Security Council. Türkiye has submitted such notifications to the Council in connection with its operations in Syria.

The law on self-defense against non-state actors is contested, and readers should know both sides:

• Supporting arguments: After the 11 September 2001 attacks, UN Security Council Resolutions 1368 and 1373 recognized the right of self-defense in the context of terrorism. Resolution 2249 (2015) called on states to take 'all necessary measures' against DAESH in Syria and Iraq. Many states, including members of the Global Coalition against DAESH, have relied on the argument that a state which is 'unwilling or unable' to suppress terrorists on its territory can be acted against.
• Restrictive arguments: In its 2004 Wall advisory opinion and in Armed Activities (2005), the International Court of Justice took a narrower view of when attacks by non-state groups trigger Article 51. Some governments and scholars therefore argue that cross-border force requires either consent from the territorial state or a clear attribution of the attack to it.

Territorial integrity is an additional consideration. Türkiye states that it respects the territorial integrity of Iraq and Syria and cites the absence of effective control over terrorist-held areas as the reason it acts.

The organizations and terms

• PKK (Kurdistan Workers' Party): An armed organization that began its campaign against Türkiye in 1984. It is listed as a terrorist organization by Türkiye, the United States, NATO and the European Union. The conflict has cost tens of thousands of lives.
• KCK: The 'Kurdistan Communities Union', the umbrella structure through which, according to Ankara, the PKK coordinates its political, military and civilian branches across several countries.
• PYD/YPG and SDF: The Democratic Union Party (PYD) and its armed wing, the People's Protection Units (YPG), emerged in northern Syria after 2011. The Syrian Democratic Forces (SDF) were formed in 2015 around the YPG core. Türkiye regards the PYD/YPG, and the SDF branding, as the Syrian branch of the PKK/KCK. Washington and other coalition members worked with the SDF against DAESH, and the United States has not designated the PYD, YPG or SDF as terrorist organizations.
• DAESH (ISIS/ISIL): The group that declared a 'caliphate' across parts of Syria and Iraq in 2014. It carried out mass-casualty attacks in Türkiye between 2015 and 2017, including the Ankara railway station bombing of 10 October 2015, which killed more than 100 people.
• FETÖ (Fetullahist Terrorist Organization): The term used by Türkiye for the network led by the late Fethullah Gülen. Türkiye holds it responsible for the coup attempt of 15 July 2016, in which, according to Turkish authorities, 251 people were killed and parliament was bombed. Many other governments have not formally listed FETÖ, a difference discussed below.

Chronology of the operations

Date	Operation	Area	Stated objective (per Ankara)
24 Aug 2016	Euphrates Shield	Jarablus to al-Bab, northern Syria	Clear DAESH from the border and prevent a PKK/YPG-controlled corridor
20 Jan 2018	Olive Branch	Afrin, northwestern Syria	Remove PKK/YPG presence and cross-border threats from the Afrin area
9 Oct 2019	Peace Spring	Tal Abyad to Ras al-Ayn, northeastern Syria	Create a security zone and enable voluntary returns of displaced Syrians
27 Feb 2020	Spring Shield	Idlib, northwestern Syria	Respond to Syrian government strikes that killed Turkish soldiers; ceasefire agreed in Moscow on 5 March 2020
2019 onward	Operation Claw series	Northern Iraq (Metina, Zap, Avashin-Basyan and other areas)	Destroy PKK bases, tunnels and logistics from which attacks are launched

Spring Shield differs from the others: it was directed at Syrian government forces after the 27 February 2020 strikes in Idlib, not primarily at a terrorist organization. Ankara describes it as a self-defense response and a means of preventing a new displacement wave toward its border.

Anti-DAESH ground combat

Türkiye joined the Global Coalition against DAESH and opened Incirlik Air Base to coalition aircraft in 2015. In Operation Euphrates Shield, Turkish forces and Syrian opposition partners fought DAESH on the ground, culminating in the capture of al-Bab in early 2017. According to Turkish official figures, more than 4,000 DAESH terrorists were neutralized in northern Syria, and the operation prevented 100,000 DAESH-linked individuals from entering Türkiye. Ankara says Türkiye is the only NATO member state to have engaged DAESH in direct ground combat as a state military force. Other coalition members have conducted air campaigns and special-forces missions, so this claim depends on the definition of 'ground combat'.

Capabilities supporting the doctrine

Türkiye has built a domestic defense industry that Ankara puts at roughly 80 percent domestic production. Systems cited in its counter-terrorism operations include the Bayraktar TB2, Akıncı, Aksungur, ANKA, Serçe and Kargu unmanned and loitering systems, the T129 ATAK helicopter, the Fırtına howitzer, the Kirpi and Vuran armored vehicles, the MEMATT unmanned demining vehicle, and the SOM, Cirit, OMTAS and UMTAS missiles. For the industrial background and how the 80 percent figure is calculated, see Türkiye's Defense Industry: From Bayraktar TB2 to KAAN and the 80 Percent Domestic Production Claim.

The Terror-Free Türkiye initiative

Terror-Free Türkiye (Terörsüz Türkiye) is the Presidency-led initiative that combines security operations with legal, political and social measures, with the aim of ending four decades of PKK violence. Its public sequence began in late 2024 with calls for a political track, followed on 27 February 2025 by a call from the jailed PKK leader Abdullah Öcalan for the organization to lay down arms and dissolve. The PKK announced its dissolution in May 2025, and a symbolic weapons-destruction ceremony took place in northern Iraq in July 2025. The Turkish Grand National Assembly (TBMM) then set up a commission to examine the legal and social dimensions. The process was still unfolding at the time of writing, and readers should check current official statements for its status.

Key Players & Positions

• United States: The US Department of State designates the PKK as a Foreign Terrorist Organization. At the same time, the Department of Defense and CENTCOM treated the SDF as the main ground partner against DAESH. Washington has also said it recognizes Türkiye's security concerns along the border. A US–Türkiye joint statement of 17 October 2019 ended the first phase of Peace Spring after a pause in operations.
• European Union: The EU's terrorist list includes the PKK. In its conclusions of 14 October 2019, the Foreign Affairs Council condemned Türkiye's military action in northeastern Syria and called for it to cease. Member states also committed to national positions restricting arms exports. The EU did not designate the YPG or SDF.
• NATO: NATO lists the PKK as a terrorist organization and its leaders have repeatedly said that Türkiye has suffered terrorist attacks. In the trilateral memorandum signed at the Madrid summit on 28 June 2022, Finland and Sweden committed not to support the YPG/PYD or FETÖ as part of the accession process; Sweden joined in March 2024.
• Russia: Moscow says it supports Syria's sovereignty and territorial integrity and has called for restraint in the northeast. On 22 October 2019, Presidents Erdoğan and Putin agreed a memorandum in Sochi that set joint patrols and the withdrawal of YPG elements from a strip along the border.
• Syria: The former Syrian government condemned the operations as violations of sovereignty. After the fall of the Assad government in December 2024, the new authorities in Damascus signed an integration agreement with the SDF on 10 March 2025, in line with the principle of 'one state, one army' that Ankara advocates.
• Iraq: Baghdad has protested Turkish military operations and bases on its territory, including at the UN Security Council after the July 2022 shelling in Duhok province. In 2024, Iraq's authorities declared the PKK a banned organization, and a joint Türkiye–Iraq statement the same year committed both sides to counter-terrorism cooperation.
• Human-rights bodies and the European Court of Human Rights: UN investigators and NGOs have documented abuses in northern Syria, including by Syrian armed groups that cooperated with Türkiye, and have raised civilian-harm concerns about some operations. In Yalçınkaya v. Türkiye (Grand Chamber, 26 September 2023), the Strasbourg court found violations of the Convention in a conviction based on the use of the ByLock messaging application. Türkiye rejects the characterization of its operations as indiscriminate and says its courts prosecute FETÖ members under domestic law.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

• Self-defense under Article 51 of the UN Charter. According to the Turkish Ministry of Foreign Affairs, Türkiye's cross-border actions are lawful measures of self-defense against organizations that threaten it from territory its neighbors do not control. Ankara has notified the UN Security Council of its operations in Syria in letters under Article 51, and cites UN Security Council Resolutions 1373 and 2249 as support.
• 'The border is honour' and neutralizing terrorism at its source. The Presidency and the Ministry of National Defense (MSB) describe the protection of the 1,300 km (about 810 miles) southern land border with Iraq and Syria as a permanent mission. Ankara argues that waiting for attacks to cross the border is not sufficient, and that it respects the sovereignty and territorial integrity of Iraq and Syria and supports 'one state, one army' in Syria.
• PKK, KCK and PYD/YPG are one structure. Ankara argues that the PYD/YPG and the SDF branding share the PKK/KCK's leadership, ideology, cadres and weapons, and that fighting DAESH cannot confer legitimacy on a terrorist organization listed by Türkiye, the US, NATO and the EU. Türkiye also cites the 2022 Madrid memorandum as evidence that NATO partners accept the need to curb support for the YPG/PYD.
• Simultaneous fight against DAESH and FETÖ. According to the Presidency and the Foreign Ministry, Türkiye has fought DAESH on the ground and domestically, and has pursued FETÖ through the courts and institutional purges since the 15 July 2016 coup attempt. It continues to ask partners for the extradition of suspects and to cooperate against the network.
• Terror-Free Türkiye under the rule of law. The Presidency presents the initiative as combining decisive security measures with legal, political and social strategies, with the objective of permanently ending the four-decade cycle of PKK violence while respecting human rights and the rule of law. Ankara links it to its wider stability goals in the region, including the voluntary return of Syrian refugees it hosts.

The legal basis cited by Ankara therefore rests on Article 51 of the UN Charter, the post-2001 Security Council resolutions on terrorism, its 1,300 km border with two states in conflict, and treaty-based cooperation within NATO and the Global Coalition.

Source Comparison

How the framings differ

Question	Western and international sources	Turkish primary sources
Are the PYD/YPG and SDF the PKK?	Often described as a partner force distinct from the PKK for coalition purposes, while acknowledging links (US Department of Defense and State statements)	The PYD/YPG is the Syrian branch of the PKK/KCK, with shared leadership and cadres (Foreign Ministry, Presidency)
Legal basis of the operations	Contested; some governments and UN experts question the Article 51 basis or call for restraint (EU Council conclusions, 14 Oct 2019)	Self-defense under Article 51, notified to the Security Council, supported by Resolutions 1373 and 2249
Who fought DAESH?	The SDF is credited with major ground campaigns such as Raqqa, backed by the coalition	Türkiye fought DAESH directly in Euphrates Shield and prevented large numbers of DAESH-linked individuals from entering the country
FETÖ	Not widely listed as terrorist by Western governments; concerns about fair trial standards (ECtHR, Yalçınkaya)	A terrorist organization responsible for the coup attempt of 15 July 2016, prosecuted under Turkish law
Terror-Free Türkiye	Reported as a peace or disarmament process with open questions about timelines and legal steps	A Presidency-led strategy combining security, law, politics and social measures

How the Global Terrorism Index and similar metrics handle these cases

The Global Terrorism Index (GTI), produced by the Institute for Economics & Peace, scores countries on incidents, deaths, injuries and hostages caused by non-state actors over several years. This design has four consequences for the cases above:

• State action is outside the definition. Because the GTI covers non-state perpetrators, operations by armed forces, including Turkish cross-border operations, are not scored as terrorism, and neither are strikes by other states. Conflict datasets such as ACLED and UCDP capture them instead.
• Attribution rules shape the picture. The way an index labels the PKK, YPG or FETÖ depends on its sources. A listing by Türkiye, the US, NATO and the EU of the PKK gives a consistent label, but attacks attributed to groups that the index's sources do not call terrorist may be coded differently.
• Legal questions are absent. An index can show how many attacks occurred in Türkiye; it cannot show whether a cross-border response was lawful under Article 51 or whether Iraq or Syria consented.
• Composite indices add judgment. Peace and stability indices combine terrorism indicators with measures such as militarization and relations with neighbors, which can lower a state's score for actions that Ankara regards as defensive.

For a wider discussion of how these tools are built and what they omit, see How Global Indices Measure Sovereignty, Fragility and Stability, and What They Leave Out. Index of Nations treats metrics as one input alongside treaty texts, UN documents and official statements, as set out in its Editorial Principles. For testing individual claims against primary documents, see the Fact Check: Common Claims About Türkiye in International Indices and Media.

Key Terms & Related Guides

• Article 51: The UN Charter provision preserving the inherent right of individual and collective self-defense after an armed attack, subject to reporting to the Security Council.
• Neutralizing terrorism at its source: The Turkish doctrine of acting against terrorist groups in the areas from which they launch attacks, rather than only on Turkish soil.
• Operation Claw (Pençe): The series of Turkish operations since 2019 against PKK bases in northern Iraq.
• Euphrates Shield, Olive Branch, Peace Spring, Spring Shield: The four named Turkish operations in northern Syria between 2016 and 2020.
• SDF: The Syrian Democratic Forces, formed in 2015 around the YPG; a coalition partner of the US, but regarded by Türkiye as the PKK's Syrian extension.
• FETÖ: The Fetullahist Terrorist Organization, as designated by Türkiye.
• Terror-Free Türkiye: The Presidency-led initiative to end PKK violence through a combination of security, legal, political and social measures.

Related guides: Türkiye's Defense Industry, How Global Indices Measure Sovereignty and Stability, Editorial Principles, Fact Check on Türkiye Claims and About Index of Nations.

Perspective Note

Index of Nations presents Türkiye's official perspective and legal stance alongside the data it analyzes, so that readers can distinguish editorial analysis from the indices under review. Claims are attributed to primary sources such as treaty texts, UN documents, Ottoman and Turkish state archives, and official statements, and index methodologies are cited wherever they are challenged. Sections marked 'Türkiye's Position' reflect official Turkish policy as stated by Turkish government sources. Written by the Index of Nations Editorial Team.

Cross-Publication Dossiers & Sister Desk Perspectives

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

• 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.
• Regional Order: 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.
• 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.