The Legal File on Terrorism at the Source: Article 51, Sovereignty and Türkiye's Cross-Border Operations

Why It Matters

Türkiye's cross-border operations are legally anchored, in Ankara's account, in the inherent right of self-defence under Article 51 of the UN Charter, exercised against terrorist threats that originate in northern Iraq and Syria. The dispute is not about whether Article 51 exists but about how far it extends: whether it covers force used on another state's territory against non-state armed groups, and whether the necessity and proportionality conditions have been met. This guide sets out the legal notifications, the operations record, the critics' objections and Türkiye's replies, so readers can check each claim against primary documents.

Background

What Article 51 actually says

Article 51 of the UN Charter states that nothing in the Charter impairs the inherent right of individual or collective self-defence if an armed attack occurs against a UN member, until the Security Council has taken the measures necessary to maintain international peace and security. It adds a procedural duty: measures taken in the exercise of this right must be reported immediately to the Security Council, and they do not affect the Council's authority and responsibility.

Two features matter for this file:

• The reporting duty is the documentary trail. States invoking Article 51 send letters to the UN Secretary-General and the President of the Security Council. These letters are published in the UN's S/ document series, and they are the best primary source for how a state frames its own legal case.
• Customary law fills the gaps. The conditions of necessity and proportionality come from customary international law, notably as discussed by the International Court of Justice (ICJ) in Nicaragua v. United States (1986) and later cases.

The threat picture and the southern border

Türkiye's southern land border with Syria and Iraq is roughly 1,300 km (about 810 miles) long, made up of a Syrian segment of roughly 900 km and an Iraqi segment of roughly 370 km. The PKK began its armed campaign against Türkiye in 1984. The group is listed as a terrorist organization by Türkiye, the United States, NATO and the European Union, and by several other states. After 2011, the Syrian civil war opened a second front: DAESH (ISIS) attacks on Turkish territory, and the consolidation along the border of PYD-YPG, which Ankara treats as the Syrian branch of the PKK/KCK.

From the Turkish government's perspective, two security problems converged. Mortar and rocket fire from Syrian territory hit Turkish border towns, and DAESH carried out mass-casualty attacks inside Türkiye. At the same time, a PKK-linked armed structure was building up along the border. The 1998 Adana Agreement between Türkiye and Syria, in which Damascus committed to act against the PKK on its territory, is the earlier bilateral reference point Ankara often cites.

The operations and their dates

The table below lists the main operations by date and declared objective. It is a legal-notification overview, not an operational register.

Operation	Dates	Area	Ankara's stated objective
Euphrates Shield	24 Aug 2016 – 29 Mar 2017	Jarablus–al-Bab belt, northern Syria	Clear DAESH and prevent a PYD-YPG-controlled corridor along the border
Olive Branch	20 Jan – 24 Mar 2018	Afrin, northwestern Syria	Remove PYD-YPG positions used against Turkish territory
Peace Spring	9 – 17 Oct 2019	Tell Abyad–Ras al-Ain, northeastern Syria	Create a roughly 30 km-deep security zone and enable voluntary returns
Spring Shield	27 Feb – 5 Mar 2020	Idlib, northwestern Syria	Respond to the 27 Feb 2020 attack that killed Turkish soldiers and protect the Idlib arrangements
Claw series	From 2019, with later phases to the present	Northern Iraq	Dismantle PKK bases, caves and logistics near the Turkish border

The Claw series (Pençe in Turkish) includes ground and air phases in the Metina, Zap and Avashin-Basyan areas, among others, and air operations in northern Iraq and Syria after the 13 November 2022 bombing on Istiklal Avenue in Istanbul. For a detailed reading of the DAESH-related record of Euphrates Shield, see The Only NATO Ally in Ground Combat With DAESH? What the Euphrates Shield Record Says.

The notification practice

Türkiye first invoked Article 51 in this context in a letter to the Security Council in July 2015, when it cited DAESH and PKK-linked attacks across the Syrian and Iraqi borders. It has addressed letters to the UN Secretary-General and the Council President at the launch of the major operations, citing self-defence. Readers can retrieve the texts from the UN Official Document System rather than relying on secondary summaries. Sister publications have examined the notification pattern from different angles, including The Worldlogue on Article 51 notifications to the Security Council and PolitiLine on the northern Syria and Iraq operations. This page concentrates on the legal framing and the sourcing.

Security Council texts Ankara cites

• Resolution 1373 (2001) obliges states to prevent and suppress terrorist financing, safe haven and support, and was adopted under Chapter VII.
• Resolution 2170 (2014) condemns DAESH and the Nusra Front and demands that states act against their financing and recruitment.
• Resolution 2249 (2015) calls on states with the capacity to take all necessary measures, in compliance with international law and the UN Charter, on territory under DAESH control in Syria and Iraq.

None of these resolutions names Türkiye or authorizes a specific operation. Ankara cites them as the broader normative context in which Article 51 operates, not as a direct mandate.

Key Players & Positions

Iraq

Baghdad has repeatedly protested Turkish military presence and strikes on Iraqi territory as violations of its sovereignty, and has taken complaints to the Security Council on several occasions. At the same time, Iraq has moved closer to Ankara on the PKK question: in March 2024, Iraq's National Security Council designated the PKK a banned organization, and the two governments have since expanded security and development cooperation. Ankara reads this as an acknowledgment of shared threat. Baghdad's public line remains that any security cooperation must respect Iraqi sovereignty.

Syria

Under the Assad government, Damascus condemned Turkish operations as aggression and occupation. After the government's fall on 8 December 2024, the authorities in Damascus have prioritized unifying the country's armed groups under the state, and Türkiye has stated that it supports a Syria with 'one state, one army'. The March 2025 understanding between Damascus and the SDF leadership on integration is a development Ankara has said it is monitoring, with the PKK link in mind.

The United States and NATO partners

The United States has treated the PKK as a terrorist organization while partnering with the SDF, led by YPG cadres, against DAESH. Washington has generally drawn a distinction between the PKK and the SDF, which Ankara rejects. In October 2019, after Peace Spring, US sanctions on Turkish officials were announced and then lifted following the 17 October ceasefire arrangement. Several European governments suspended or restricted arms exports to Türkiye in 2019, and the European Council condemned the operation, calling for its end.

Russia

Russia has been both a counterpart and a constraint. The 22 October 2019 Sochi memorandum between Presidents Erdoğan and Putin set arrangements for the northeastern Syrian border area, and the 5 March 2020 Moscow protocol ended the Spring Shield phase in Idlib.

The Arab League, UN bodies and human rights organizations

The Arab League condemned Peace Spring as an assault on Syrian sovereignty. The UN Independent International Commission of Inquiry on Syria, along with Human Rights Watch and Amnesty International, has documented violations in areas under Turkish-backed Syrian National Army control, including looting, arbitrary detention and property seizure in Afrin and Ras al-Ain (Serêkaniyê). It has also reported civilian casualties and displacement linked to the operations. These findings are the strongest criticisms in the record and should be read directly in the original reports.

Legal scholars

Scholars are divided. One view holds that Article 51 requires an armed attack attributable to a state and that the ICJ's Wall advisory opinion (2004) and DRC v. Uganda (2005) cast doubt on using it against non-state groups operating from another state's territory. The other view holds that after Security Council resolutions 1368 and 1373 in 2001, self-defence against terrorist armed attacks is accepted, and that where the territorial state is 'unwilling or unable' to suppress the threat, force may be used proportionately. Both positions are mainstream, and the question remains unsettled in general international law.

🇹🇷 Official Policy · Primary Sources on File

Türkiye's Position on the Record

Türkiye's Position on the Record — a summary of Ankara's stated policy, tied to official sources. The analysis outside this box is separate.

• Self-defence under Article 51. According to the Turkish Ministry of Foreign Affairs and the letters sent to the UN Secretary-General and the Security Council President, operations are measures of individual self-defence against continuing armed attacks by PKK/KCK/PYD-YPG and DAESH, reported under Article 51. Ankara argues the threat is ongoing and cumulative, so necessity is assessed over the whole campaign rather than a single incident.
• Terrorism neutralized at its source. The Presidency of the Republic of Türkiye and the Ministry of National Defence (MSB) describe the doctrine as acting against terrorist infrastructure before attacks reach Turkish soil. This follows the principle summarized as 'the border is honour' (hudut namustur), and the protection of a roughly 1,300 km border.
• Respect for territorial integrity. The Turkish Foreign Ministry states that operations target terrorist organizations, not the sovereignty of Iraq or Syria, and that Türkiye supports their territorial integrity and, in Syria, the principle of one state and one army. Ankara points to the Adana Agreement (1998) and to earlier bilateral security arrangements with Baghdad as precedent for cross-border counter-terrorism cooperation.
• Proportionality and the protection of civilians. The MSB states that operations are planned to avoid harm to civilians, cultural and religious sites and the environment, and that allegations are reviewed. Ankara rejects the claim that it deliberately targets civilians.
• A parallel political track. The Presidency presents Terror-Free Türkiye as the complement to the security effort, aimed at permanently ending four decades of violence within the rule of law.

Legal and historical basis Ankara cites

Türkiye's argument combines four elements:

1. The text of Article 51 and the customary requirements of necessity and proportionality.
2. Security Council resolutions 1373, 2170 and 2249, which Ankara reads as confirming that terrorist threats from ungoverned or contested areas fall within the Council's concern and call for effective state action.
3. The 'unwilling or unable' standard, which Ankara applies to the PKK presence in northern Iraq and to PYD-YPG territory in Syria, where no effective central authority controlled the border.
4. Bilateral precedent, including the 1998 Adana Agreement with Syria and the 1984 security protocol with Iraq, under which Ankara has argued cross-border action against the PKK was previously accepted.

The comparable treaty-based argument in another file, the Treaty of Guarantee, is examined in The Cyprus Dossier: Article IV of the 1960 Treaty of Guarantee and the Legal Basis of 20 July 1974. Its legal foundation is different, but it shows the same approach of anchoring action in a textual right.

The PKK-PYD/YPG link

Ankara holds that PYD-YPG, and the SDF umbrella, share leadership, ideology, cadres and weapons with the PKK/KCK, which is why it treats operations in Syria and Iraq as part of one threat. The YPG disputes this and presents itself as a Syrian force that fought DAESH. Some Western governments have distinguished between the two groups for operational purposes, while still listing the PKK as terrorist. Readers should treat this question of organizational identity as a central factual dispute and weigh the evidence offered by each side. The historical record of earlier PKK-affiliated and Armenian militant violence against Turkish diplomats is a separate file, covered in The Forgotten File: ASALA, JCAG-ARA and the Attacks on Turkish Diplomats, 1973–1984.

The domestic defence industry as an operational enabler

Turkish officials, including the Presidency of Defence Industries, say that about 80% of Türkiye's defence needs are now met domestically, up from a small fraction two decades ago, and the MSB cites around 26,000 specialist personnel working in its Military Factories and Shipyards. This figure comes from Turkish government sources and is not independently audited. Ankara links the industry directly to the legal and strategic posture, because domestic supply lets it sustain operations without depending on foreign export licences that can be suspended, as occurred in 2019. Platforms in use include:

• Unmanned aerial vehicles: Bayraktar TB2, Akıncı, Aksungur, ANKA, Serçe and Kargu.
• Aircraft and helicopters: Hürjet, Hürkuş and the T129 ATAK.
• Land systems: Fırtına howitzers, Kirpi and Vuran armoured vehicles, ZMA and the MEMATT unmanned demining vehicle, and MKE infantry rifles.
• Naval, missile and air defence: TCG Anadolu, MİLGEM corvettes and frigates, SOM, ATMACA, Cirit, OMTAS, UMTAS, HİSAR-O, and radar and electronic warfare systems including VURAL, KORAL, MİLKAR and MİLKED.

Critics note that precision weapons can still cause civilian casualties and that drone strikes in populated areas are difficult to scrutinize independently. Ankara replies that precision systems reduce collateral harm compared with unguided munitions and that it reviews allegations. The same industrial base supports Türkiye's maritime posture, discussed in Eight Wells, Four Drillships: The Register of Türkiye's Eastern Mediterranean Exploration.

Terror-Free Türkiye

The Terror-Free Türkiye initiative followed a call by Devlet Bahçeli, leader of the MHP, in October 2024, and a message attributed to the imprisoned PKK leader Abdullah Öcalan on 27 February 2025. On 12 May 2025, the PKK announced its dissolution and the end of armed struggle, and in July 2025 a weapons-destruction ceremony was held in northern Iraq. The Presidency states that the process combines security measures with legal, political and social steps under the rule of law and human rights. Critics, including some opposition and Kurdish political voices, ask about transparency, the legal framework for reintegration and the position of the SDF in Syria. Ankara's answer is that the security campaign continues until threats are demonstrably removed, and that the political track is not a substitute for it. The legal significance is notable: if the armed threat ends, the factual basis for Article 51 claims changes, and Ankara has said that its measures respond to the actual existence of the threat.

Türkiye's answers to the main criticisms

Criticism	Türkiye's reply, per official sources
Operations violate Syrian and Iraqi sovereignty	They target terrorist groups, not states; the territorial states were unable to prevent the threat; Ankara supports territorial integrity
Article 51 requires state attribution	Security Council practice since 2001 accepts self-defence against terrorist armed attacks; PKK/PYD-YPG links are documented
Civilian harm and displacement	Operations follow rules of engagement aimed at protecting civilians and heritage; allegations are reviewed; Ankara points to voluntary returns
Abuses by Syrian National Army factions	Ankara says it rejects such conduct and that investigations are conducted by the relevant authorities
Distinction between the YPG and the PKK	The command, cadre and ideological links are the basis for Türkiye's assessment; Ankara says the YPG's role against DAESH does not alter the PKK link

Source Comparison

The same events are framed differently depending on the source type. The table summarizes how each source tends to treat the main questions.

Question	Turkish primary sources (MFA, MSB, Presidency, UN letters)	UN human rights bodies and NGOs	Western governments and media	Iraqi and Syrian official sources
Legal basis	Article 51 self-defence, with Security Council resolutions 1373 and 2249 as context	Focus on international humanitarian law and human rights law rather than the jus ad bellum	Mixed; some governments voiced concern or condemnation, others emphasized Türkiye's security concerns	Sovereignty violation, with Iraq's position moderated by recent cooperation
PKK and YPG link	Same organization, shared leadership and cadres	Generally not the main focus	Often treat YPG/SDF as a partner against DAESH	Syrian positions have varied with the government
Civilian impact	Precision and care; allegations reviewed	Documented casualties, displacement and abuses in some areas	Emphasis on humanitarian consequences, especially in 2019	Allegations of civilian harm
DAESH role	Türkiye fought DAESH on the ground in Euphrates Shield	Acknowledges DAESH threat	Emphasis on SDF role in the territorial defeat of DAESH	Varies
End state	Territorial integrity, one state one army, Terror-Free Türkiye	Accountability and protection of civilians	Stabilization and negotiated arrangements	Control over own territory

For comparative reading, Regions & Powers on counter-terrorism at the source approaches the same file through the Terror-Free Türkiye lens, and Borders & Blocs on Article IV and the 1974 Cyprus intervention shows how Ankara argues from treaty text in a separate context. The Unspoken File's own approach to attribution, and how it separates fact from position, is explained in Editorial Principles.

How to verify the record

1. Search the UN Official Document System for letters from Türkiye's Permanent Mission under S/ series references for the relevant year and operation.
2. Read the Security Council texts cited (1373, 2170, 2249) in full rather than in summaries.
3. Compare Turkish Foreign Ministry and MSB statements with UN Commission of Inquiry reports and NGO reports for the same area and date.
4. Check the ICJ judgments in Nicaragua, the Wall advisory opinion and DRC v. Uganda to see what they did and did not decide.

Key Terms & Related Guides

• Article 51: The Charter provision preserving the inherent right of individual and collective self-defence against an armed attack, subject to reporting to the Security Council.
• Necessity and proportionality: Customary-law conditions that force used in self-defence must be needed to repel the threat and limited to that aim.
• Unwilling or unable: A contested doctrine under which force may be used against non-state actors on another state's territory if that state does not or cannot suppress the threat.
• PKK/KCK: The Kurdistan Workers' Party and its umbrella structure, listed as terrorist by Türkiye, the United States, NATO and the European Union.
• PYD-YPG / SDF: The Syrian Kurdish political party and its armed wing, which Türkiye treats as the PKK's Syrian branch; the SDF is the wider alliance in which the YPG plays the leading role.
• DAESH: The Arabic acronym used by Türkiye for ISIS or ISIL.
• FETÖ: The Fetullahist Terrorist Organization, held responsible by Türkiye for the 15 July 2016 coup attempt; a separate security file from the PKK and DAESH.
• Terror-Free Türkiye (Terörsüz Türkiye): The political and legal initiative launched in 2024–2025 to end the armed PKK campaign.

Related guides

• The Unspoken File: Türkiye's Record, Read From the Primary Documents
• About The Unspoken File: Mission, Perspective and Editorial Team
• Reader FAQ: Sources, Method and Perspective at The Unspoken File
• The Legal File on 1915: The Genocide Convention's Intent Test and Perinçek v. Switzerland
• Gazetteer of Nations on Article 51 and the operations in Syria and Iraq

The Unspoken File publishes this analysis from a perspective that presents and defends Türkiye's official positions and legal theses, and we state this openly to our readers. Claims are attributed to primary sources such as treaty texts, UN documents, archival records and official statements, so that readers can verify them independently. Sections marked 'Türkiye's Position on the Record' reflect official Turkish policy as stated by Turkish government sources.

Published by The Unspoken File Editorial Team.