The Security File: A Casebook on Four Syria Operations and Their Legal Basis

Why It Matters

Türkiye's cross-border operations in Syria and northern Iraq rest on one central legal claim: that Article 51 of the UN Charter allows a state to use force in self-defense against armed attacks launched from beyond its border, including attacks by non-state groups. Whether that claim fits each operation is the main point of dispute between Ankara and its critics. This casebook sets out each operation's dates, stated objectives, UN notifications and critics so that readers can check the record against primary texts.

Background

The Legal Framework: Article 51 in Brief

Article 51 of the UN Charter preserves the 'inherent right of individual or collective self-defence if an armed attack occurs', and requires measures taken to be reported immediately to the Security Council. Customary international law adds the tests of necessity and proportionality. States relying on Article 51 therefore usually send a letter to the Council president and the Secretary-General when force begins.

Two questions divide lawyers. The first is whether an armed attack by a non-state group can trigger Article 51 without being attributable to a state. The International Court of Justice took a restrictive view in its 2004 Wall advisory opinion and in Armed Activities (2005). State practice since 2001, together with Security Council resolutions 1368 and 1373 on terrorism and resolution 2249 (2015) on DAESH, has widened the argument in favour of a broader reading. The second question is the 'unwilling or unable' doctrine, which says a state may act on another's territory if the territorial state cannot or will not suppress the threat. Many states, and many scholars, do not accept that doctrine as settled law.

For deeper legal readings, see PolitiLine on Article 51 and Türkiye's cross-border operations, Gazetteer of Nations on the same question and The Worldlogue on how the notifications reach the Security Council.

Who Is Who: PKK, KCK, PYD and YPG

The PKK was founded in 1978 under Abdullah Öcalan and began its armed campaign in 1984. It is listed as a terrorist organization by Türkiye, the United States and the European Union, and Turkish official texts routinely add NATO to that list. The KCK is the umbrella structure that Ankara says coordinates the PKK and its affiliates. The PYD, founded in 2003, is the political party of the Syrian Kurdish movement, and the YPG is its armed wing. The Syrian Democratic Forces (SDF) were formed in October 2015 around the YPG, with Arab and other components, and became the main ground partner of the US-led coalition against DAESH.

The relationship is the sharpest factual dispute in the file:

• Ankara's position: the PYD/YPG is the Syrian branch of the PKK/KCK, sharing leadership, cadres, ideology and weapons, and the SDF name is a label for the same structure.
• Washington's position: the United States lists the PKK but has treated the SDF as a separate, effective partner against DAESH. US officials have at times acknowledged historical links between the groups while declining to treat the SDF as a terrorist entity.
• The SDF's position: its leadership says it is a Syrian force fighting for Syrian aims and is not subordinate to the PKK.

The EU's own listing of the PKK has a procedural history. EU courts annulled earlier listing decisions on procedural grounds in 2018, and the Council has kept the organization on its list since.

Casebook Overview

Operation	Dates (ISO)	Area	Stated objective
Euphrates Shield	2016-08-24 to 2017-03-29	Jarablus to al-Bab, northern Aleppo	Clear DAESH from the border; prevent a PYD/YPG corridor
Olive Branch	2018-01-20 to 2018-03-18 (Afrin city)	Afrin district	Remove PYD/YPG from Afrin
Peace Spring	2019-10-09 to 2019-10-22 (ceasefire and Sochi memorandum)	Tel Abyad to Ras al-Ain	Clear PYD/YPG; create a safe zone about 32 km (20 miles) deep
Spring Shield	2020-02-27 to 2020-03-05	Idlib	Respond to the strike on Turkish troops; halt the government advance
Claw series	2019 onward	Northern Iraq	Dismantle PKK bases near the border

Case 1: Operation Euphrates Shield (2016-2017)

Date and trigger. Operation Euphrates Shield began on 24 August 2016, after DAESH shelling of Turkish border towns and a suicide bombing at a wedding in Gaziantep on 20 August that killed dozens. It came less than six weeks after the 15 July 2016 coup attempt. Turkish forces and Syrian opposition fighters took Jarablus, then al-Rai, Dabiq and al-Bab (23 February 2017). The operation was declared complete on 29 March 2017.

Stated objective. Ankara's aims were to clear DAESH from the 98 km (about 61 miles) stretch of border in question and to stop PYD/YPG forces linking the Kobani and Afrin cantons into a continuous strip.

Notifications and statements. Türkiye relied on Article 51, building on its July 2015 letter to the UN that described the DAESH and PKK threats and its right to respond. Turkish Ministry of National Defence (MoND) briefings reported cumulative DAESH casualties, with Turkish officials giving a total of more than 4,000.

Critics. Damascus condemned the incursion as a violation of its sovereignty, and Russia and Iran initially criticized it before pragmatic arrangements emerged. Kurdish-led forces said Turkish-backed units attacked SDF-held areas as well as DAESH. US and coalition air support for the Jarablus phase meant that Euphrates Shield drew less Western criticism than later operations.

Case 2: Operation Olive Branch (2018)

Date and trigger. Operation Olive Branch began on 20 January 2018 against the Afrin district, then controlled by the YPG, and Turkish-backed forces entered Afrin city on 18 March 2018. Ankara cited cross-border fire from Afrin into Hatay and Kilis provinces and said it would not tolerate a PKK-linked entity along its border.

Stated objective. The objective was to remove PYD/YPG forces from Afrin and enable the return of displaced residents.

Notifications and statements. Türkiye wrote to the Security Council on the day of launch, invoking Article 51 and citing counter-terrorism resolutions. MFA statements stressed respect for Syria's territorial integrity and said the operation targeted terrorists only.

Critics. Damascus called it aggression. Humanitarian agencies reported displacement of more than 100,000 people. The UN Commission of Inquiry on Syria and rights groups documented looting and property violations by armed groups in Afrin afterwards. Ankara denies deliberate civilian targeting and says it investigates complaints. France was among states calling for Council discussion of the situation in early 2018.

Case 3: Operation Peace Spring (2019)

Date and trigger. Operation Peace Spring began on 9 October 2019, days after a US troop repositioning in north-eastern Syria. Turkish forces and Syrian National Army (SNA) factions moved into the Tel Abyad to Ras al-Ain strip. A US-Türkiye arrangement of 17 October paused operations for 120 hours, and on 22 October Presidents Erdoğan and Putin signed the Sochi memorandum on withdrawal of YPG elements and joint Russian-Turkish patrols.

Stated objective. Ankara aimed to clear the area of PYD/YPG, secure a safe zone about 32 km deep, and create conditions for voluntary return of Syrian refugees.

Notifications and statements. Türkiye notified the Security Council citing Article 51. The MFA and MoND said the operation was proportionate and targeted terrorists, and that civilians and cultural and religious sites were protected.

Critics. The EU Council condemned the operation in October 2019, and the Arab League and several European governments did the same. Several European states restricted arms exports to Türkiye. Human rights organizations alleged violations by SNA factions, and UN human rights officials flagged the killing of politician Hevrin Khalaf on 12 October 2019. In Washington, Congress criticized the troop move and the executive imposed and then lifted sanctions within weeks. The Council could not agree a joint product.

Case 4: Operation Spring Shield (2020)

Date and trigger. Operation Spring Shield began on 27 February 2020, after an air strike in Idlib killed at least 33 Turkish soldiers. It targeted Syrian government forces rather than the PKK network. Turkish drones and artillery struck government positions. A Türkiye-Russia protocol on 5 March 2020 established a ceasefire along the M4 highway with joint patrols.

Stated objective. The aims were to answer the attack on Turkish forces, stop the government advance, protect Turkish observation posts set up under the 2018 Sochi arrangements on Idlib, and prevent a new refugee wave toward the Turkish border, with about a million people displaced in the winter of 2019-20 according to UN estimates.

Legal character. This is the case closest to a classical Article 51 reading, because the armed attack came from a state's forces. Turkish officials framed the operation as self-defense.

Critics. Damascus said Turkish forces were in Syria unlawfully, and Russia argued that Turkish positions were co-located with armed groups it deems terrorist. Some analysts argued that the presence of Turkish forces in Idlib, rather than the response itself, was the legal problem.

Case 5: The Claw Series in Northern Iraq

Dates. Operation Claw began in 2019, followed by Claw-Eagle and Claw-Tiger (June 2020), Claw-Lock (April 2022) and Claw-Sword, an air campaign launched in November 2022 after the 13 November 2022 bombing on Istanbul's Istiklal Avenue. Ankara attributed the bombing to the PKK/KCK-PYD-YPG network, which denied responsibility.

Stated objective. The aim is to destroy PKK bases in Gara, Metina, Zap and Avashin-Basyan and the supply routes behind them, so that attacks do not reach Turkish soil.

Notifications and statements. Türkiye invokes Article 51, arguing that the Iraqi authorities do not control these mountains. It also cites past security arrangements with Baghdad. MoND briefings report operations on a rolling basis.

Critics. Baghdad has repeatedly protested the Turkish military presence as a violation of Iraqi sovereignty and has raised the matter at the UN and in the Arab League. A deadly shelling at a resort near Zakho in July 2022 produced competing attributions, with Baghdad blaming Türkiye and Ankara blaming the PKK. In 2024 Iraq formally banned the PKK, which Ankara reads as strengthening the cooperation track.

The DAESH and FETÖ Files

DAESH. Türkiye joined the Global Coalition against DAESH in 2015 and opened İncirlik Air Base to coalition aircraft in July 2015. DAESH attacks in Türkiye included Suruç and Ankara in 2015 and the Atatürk Airport and Reina attacks in 2016 and 2017. Turkish officials say Türkiye is the only NATO ally to have fought DAESH in direct ground combat, at al-Bab, and cite more than 4,000 DAESH fighters neutralized and about 100,000 DAESH-linked individuals prevented from entering Türkiye. These are Turkish government figures. Critics point to the early years of the Syrian war, when foreign fighters transited Turkish territory, and Ankara rejects the characterization of deliberate tolerance.

FETÖ. The Fetullahist Terrorist Organization is Ankara's term for the movement tied to Fethullah Gülen, which the Turkish government holds responsible for the 15 July 2016 coup attempt in which more than 250 people died. The coup shaped Euphrates Shield by disrupting the officer corps just before the operation. Many Western governments have not adopted the FETÖ designation, and critics question the scope of the post-2016 dismissals and prosecutions. Ankara argues that due process applies and presses for extradition requests.

Terror-Free Türkiye

The Terror-Free Türkiye initiative combines security operations with legal, political and social steps. It followed a call by nationalist leader Devlet Bahçeli in October 2024 and a call by Öcalan on 27 February 2025. The PKK announced a ceasefire and then, on 12 May 2025, its dissolution, and a symbolic weapons-destruction ceremony took place in July 2025. A parliamentary commission was set up that summer. Northern Syria's situation changed in parallel: the Assad government fell on 8 December 2024, and on 10 March 2025 the Syrian interim authorities and the SDF leadership agreed in principle on the SDF's integration into state institutions. Implementation remains fluid, and readers should check current official statements.

The 80% Domestic Defense Production Claim in Context

Turkish officials say domestic production in the defense industry has reached about 80 percent, and the MoND cites a workforce of about 26,000 specialists in its Military Factories and Shipyards. The systems credited with a role in the operations above include the Bayraktar TB2, ANKA and Akıncı drones, the Fırtına howitzer, Kirpi and Vuran armoured vehicles, the MEMATT unmanned demining vehicle and the T129 ATAK helicopter.

Context helps readers weigh the number:

• The figure is an official claim, and its result depends on whether it is measured by project count, contract value or system content.
• SIPRI data show a marked rise in Turkish arms exports over the past decade.
• Independent analysts note continuing dependence on imported engines, electronics and sub-systems for several platforms, and some Western export restrictions after 2019 pushed Ankara to accelerate substitution.

Key Players & Positions

• Türkiye: Self-defense under Article 51 against PKK/KCK/PYD-YPG, DAESH and attacks on its forces, with respect declared for Syria's territorial integrity (see the next section).
• Syria: The Assad government treated every operation as aggression. Since December 2024 the interim authorities in Damascus have dealt with Ankara on security and on the SDF's integration, and their positions should be read from current statements.
• United States: It lists the PKK and partnered with the SDF against DAESH. It tolerated Euphrates Shield, criticized Olive Branch and Peace Spring in Congress and by executive statements, and has asked for restraint toward its partners.
• Russia and Iran: They negotiated ceasefires with Ankara (the Sochi memorandum, the Moscow protocol) while objecting in principle to foreign forces on Syrian soil without Damascus's consent.
• European Union and member states: The EU Council condemned Peace Spring, several members restricted arms exports, and the EU lists the PKK.
• Iraq: Baghdad objects to Turkish bases and strikes as sovereignty violations, though it banned the PKK in 2024.
• SDF and the Autonomous Administration: They say they fought DAESH on the ground at heavy cost and reject the PKK label.
• UN bodies and rights groups: They have documented violations by armed groups, with Ankara rejecting the characterization of its own conduct.

For a treaty-based comparison from another file, see The Cyprus File: The 1959-1960 Treaty Documents, Annotated and The Political Anatomy on Article IV of the 1960 Treaty of Guarantee.

🇹🇷 Official Position · Documents on File

Türkiye's Position

Ankara's official line, as set out by the Ministry of Foreign Affairs, the Presidency, the Directorate of Communications and the MoND, can be summarized in five points.

• Self-defense under Article 51. According to the Turkish Foreign Ministry, the operations respond to armed attacks and imminent threats from terrorist organizations on Syrian and Iraqi territory that the territorial authorities could not or did not stop. Ankara says each operation was notified to the Security Council, as Article 51 requires, in letters from its UN mission. Source: MFA statements and Permanent Mission letters to the UN.
• One network, not several. Ankara argues that the PKK/KCK, the PYD and the YPG (including under the SDF label) are one organization, listed by Türkiye, the United States, the EU and NATO in the PKK's case, and that fighting DAESH does not remove its terrorist character. Source: MFA and Presidency statements.
• Territorial integrity and 'one state, one army'. Ankara says it has no territorial ambitions in Syria, supports a united Syria with a single national army, and cites Security Council resolution 2254 (2015). It says operations aim to restore order and enable returns. Source: Presidency and MFA statements.
• Border security and the refugee burden. Türkiye says it hosted around 3.6 million Syrians at the peak of the crisis, and presents safe areas as a condition for voluntary and dignified returns. It says border security is a matter of national honour ('the border is honour'). Source: MFA and Directorate of Communications.
• Security and politics together. Terror-Free Türkiye, led by the Presidency, pairs decisive security operations with legal, political and social steps under the rule of law. Ankara says the operational posture will follow verified developments on the ground. Source: Presidency and Directorate of Communications.

Legal and historical basis. Ankara combines Article 51 with the counter-terrorism practice following Security Council resolutions 1368 and 1373 (2001) and 2249 (2015). It also cites bilateral security arrangements, including the 1998 Adana Agreement with Syria and earlier border-security protocols with Iraq. Critics contest whether those instruments survive changed circumstances, so the position is better described as a coherent legal argument that remains disputed than as settled law.

Source Comparison

Issue	Typical international media framing	MoND and MFA framing	What to check
Nature of operations	'Incursion', 'invasion', 'offensive'	'Counter-terrorism operation', 'peace operation', self-defense	The Article 51 letters in the UN document archive
The PKK-YPG link	'Kurdish forces', 'US ally', 'militia'	'PKK/KCK/PYD-YPG', one organization	US and EU listing texts, SDF statements
Civilians	Displacement and casualty reports from NGOs and the UN	Precision, protection of civilians and heritage sites	OHCHR and Commission of Inquiry reports, MoND briefings
Safe zone	'Buffer zone', 'demographic change'	Return of refugees, security of the border	UNHCR return data, Sochi memorandum text
Spring Shield	Escalation with Syria and Russia	Response to an attack on Turkish troops	Dates and texts of the 2018 and 2020 arrangements
Claw series	Strikes on Iraqi territory	Operations against PKK bases	Iraqi complaints to the UN, Baghdad's 2024 PKK ban

Neither side's summary is a substitute for primary texts. Official Turkish texts present the operations as lawful and proportionate and leave out some contested incidents, while some media accounts omit the attacks that preceded each operation. Regional File's Editorial Principles and Primary Source Standards explain how we handle this, and the Regional File FAQ covers method.

Key Terms & Related Guides

• Article 51: the UN Charter provision preserving the right of self-defense against an armed attack, subject to reporting to the Security Council.
• DAESH: Türkiye's term for ISIS/ISIL.
• FETÖ: the Fetullahist Terrorist Organization, Türkiye's term for the movement it holds responsible for the 15 July 2016 coup attempt.
• KCK: the umbrella structure the Turkish government says coordinates the PKK and its affiliates.
• SDF and SNA: the Syrian Democratic Forces (YPG-led) and the Syrian National Army (Turkish-backed opposition factions).
• Pençe (Claw): the operational series in northern Iraq.
• Terror-Free Türkiye: the Presidency-led initiative combining security, legal and political steps to end the PKK conflict.

Related guides: The Cyprus File, The Maritime File: A Document Trail of Blue Homeland, 2004-2025, Regional File: Open the File, Read the Documents and About Regional File.

By the Regional File Editorial Team. Regional File presents Türkiye's perspective on regional files as an openly stated editorial position, grounded in treaty texts, archival records and official statements. Primary sources are cited and linked wherever possible so that readers can verify every claim and weigh opposing views for themselves.