Middle East and Caucasus Observer: Article 51, Border Security and Türkiye's Regional Deterrence

Why It Matters

Türkiye justifies its cross-border operations in northern Iraq and northern Syria as an exercise of the inherent right of self-defence under Article 51 of the UN Charter. Ankara's operational doctrine is to neutralize terrorism at its source, before attacks reach Turkish soil. The legal basis is contested: Iraq, the former Syrian government, EU institutions and human-rights bodies have raised objections, while the United States has combined a PKK terrorist designation with a partnership with the Syrian Democratic Forces (SDF).

The stakes have changed since December 2024. The Assad government fell, the PKK announced its dissolution in May 2025, and Ankara launched the Terror-Free Türkiye initiative. This guide sets out the facts, the actors' stated positions and Türkiye's official legal case, and it keeps Ankara's assessments in a clearly labelled section.

Background

What Article 51 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 necessary measures. It also requires that measures taken in exercise of this right be immediately reported to the Council. Article 2(4) prohibits the threat or use of force against the territorial integrity or political independence of any state, so every cross-border operation is judged against both provisions.

Three questions run through the debate:

• Armed attack by a non-state actor. After the attacks of 11 September 2001, Security Council Resolutions 1368 and 1373 recognized the right of self-defence in the face of terrorism. Some jurists, citing the International Court of Justice's 2004 Wall advisory opinion and its 2005 DRC v. Uganda judgment, argue that Article 51 presupposes an attack attributable to a state. Others point to state practice since 2001 as having broadened the right.
• The host state's role. Several governments, including Türkiye, support an 'unwilling or unable' reading. Under it, a state may act against a threat on foreign territory if the territorial state cannot or will not suppress it. Critics say this reading is not settled law.
• Necessity and proportionality. Even where Article 51 applies, force must be necessary, proportionate and directed at the threat. Independent monitors assess this operation by operation.

Chronology of the main operations

Period	Operation	Area	Stated Turkish aim
24 Aug 2016 – 29 Mar 2017	Euphrates Shield	Jarablus–al-Bab, northern Syria	Clear DAESH from the border and prevent a PKK/YPG-held corridor
20 Jan – Mar 2018	Olive Branch	Afrin, northwestern Syria	Remove PYD/YPG presence on the border and secure Turkish territory from attacks
From 9 Oct 2019	Peace Spring	Tel Abyad–Ras al-Ayn, northeastern Syria	Create a security zone along the border and enable voluntary returns
Feb – Mar 2020	Spring Shield	Idlib, northwestern Syria	Respond to attacks on Turkish forces (including the 27 Feb 2020 Balyun airstrike) and stop a new displacement wave
From 2019 (series)	Claw, Claw-Eagle, Claw-Tiger, Claw-Lock, Claw-Sword and others	Northern Iraq	Dismantle PKK bases, tunnels and logistics in the Kurdistan Region of Iraq

Spring Shield differs in character from the others. It followed deadly strikes on Turkish troops in Idlib, which Ankara attributed to Syrian government forces, and ended with the 5 March 2020 Moscow protocol agreed with Russia. It was not directed mainly at a non-state group.

The PKK/KCK/PYD-YPG relationship

The PKK (Kurdistan Workers' Party) began its armed campaign against Türkiye in 1984. It is designated a terrorist organization by Türkiye, the United States, NATO and the European Union. The KCK is its umbrella structure. Türkiye holds that the PYD and its armed wing, the YPG, are the Syrian branch of the PKK/KCK. It cites shared ideology, leadership and cadres, and the leadership base in the Qandil mountains. It also points to Abdullah Öcalan's role as ideological reference for the movement.

The SDF, formed in 2015, is led by the YPG. Its leaders say the SDF is a Syrian force and not a PKK subsidiary. Washington has formally maintained both positions: the PKK remains a Foreign Terrorist Organization, and the SDF was its operational partner against DAESH. Many US officials have nevertheless acknowledged organizational links between the YPG and the PKK. This gap in recognition is the main source of friction between Ankara and Washington on Syria.

DAESH and FETÖ

DAESH (the Arabic acronym for ISIS) carried out major attacks on Turkish soil in 2015 and 2016, including the Suruç, Ankara and Gaziantep bombings. Turkish officials say that more than 4,000 DAESH militants were neutralized during Euphrates Shield and that around 100,000 DAESH-linked individuals were prevented from entering Türkiye. These are Turkish official figures. Ankara also presents itself as the only NATO ally to have fought DAESH in direct ground combat, a claim examined in Is Türkiye the Only NATO Ally to Fight DAESH on the Ground? Euphrates Shield in Context.

FETÖ (the Fetullahist Terrorist Organization) is the term Türkiye uses for the network it holds responsible for the 15 July 2016 coup attempt. It is a mainly domestic and diplomatic file rather than a cross-border military one. Ankara nevertheless treats it as part of one security picture, because the coup attempt, DAESH attacks and PKK violence converged in 2015–2016 and shaped the decision to act beyond the border.

The 2024–2025 turning point

The sequence since late 2024 is as follows:

• In October 2024, Devlet Bahçeli, leader of the MHP (a partner in the governing alliance), floated a new approach to the PKK issue.
• On 27 February 2025, Abdullah Öcalan called on the PKK to lay down arms and dissolve.
• On 12 May 2025, the PKK announced it was dissolving itself.
• In July 2025, a symbolic weapons-destruction ceremony took place in the Kurdistan Region of Iraq.
• The Grand National Assembly of Türkiye (TBMM) then convened a parliamentary commission to examine the legal and political framework of the process.

In Syria, the Assad government fell on 8 December 2024. Syria's transitional authorities and the SDF signed an integration framework on 10 March 2025, and its implementation has remained fluid. SDF commander Mazloum Abdi has said the PKK process does not directly concern the SDF. Ankara says the YPG-led structure must be integrated into Syria's state institutions or dissolved. Readers should check the latest developments, as this file is moving quickly.

Key Players & Positions

United States

The US designated the PKK a Foreign Terrorist Organization in 1997. Washington has repeatedly said Türkiye has legitimate security concerns about PKK terrorism. It also partnered with the SDF against DAESH from 2014–2015 onward. In October 2019 it withdrew forces from part of the border area ahead of Peace Spring and then brokered a pause with Ankara on 17 October 2019. Since 2025, US policy has moved toward supporting SDF integration into a unified Syrian state.

European Union and member states

The EU has listed the PKK as a terrorist organization since 2002. In October 2019 the Foreign Affairs Council and European Council conclusions condemned Türkiye's military action in northeastern Syria. They called for its cessation and urged national restraint on arms exports, and several member states suspended licences. The EU also says it recognizes Türkiye's security concerns and its hosting of refugees. The European Parliament has adopted critical resolutions on specific operations.

Syria

Under the Assad government, Damascus described Turkish operations as violations of Syrian sovereignty and occupation, and it sent protests to the UN. The Adana Agreement of 1998 had previously committed Syria to act against the PKK. Ankara cites this as precedent for security cooperation. The post-Assad transitional authorities have a closer working relationship with Ankara. They also assert that all armed forces must come under a single state command.

Iraq

Baghdad has long said that Turkish strikes and ground deployments in northern Iraq violate Iraqi sovereignty. The Iraqi foreign ministry has summoned Turkish envoys and lodged complaints with the Security Council, notably after civilian deaths at the Zakho resort in July 2022. Türkiye denied responsibility for that incident and blamed the PKK. In March 2024 Iraq's National Security Council declared the PKK a banned organization, and Türkiye and Iraq have since increased security coordination. The Kurdistan Regional Government has voiced concern about civilian harm and displacement in border areas.

Human-rights bodies

The UN Independent International Commission of Inquiry on Syria, Amnesty International and Human Rights Watch have documented civilian casualties and abuses connected to Turkish operations in Syria. They have also documented abuses by Syrian armed factions allied with Türkiye in areas under Turkish influence. Some argue that Türkiye bears responsibility for violations in areas under its effective control, including water-supply interruptions at the Alouk station in Hasakah. NGOs have also reported civilian harm and displacement in the Kurdistan Region of Iraq. Türkiye rejects these characterizations. It says it takes precautions to avoid civilian harm and that complaints are investigated.

Russia and Iran

Russia and Iran, as Syria's main external backers under the Astana format, have generally called for respect for Syrian territorial integrity. They have also negotiated practical arrangements with Türkiye, for example the 22 October 2019 Sochi memorandum on joint patrols along the Peace Spring border area.

🇹🇷 Official Policy · Primary Sources

Türkiye's Position

The following points reflect official Turkish policy as stated by Turkish government sources. They are Ankara's assessments, not independent findings.

• Article 51 and notification to the Security Council. Ankara argues that continuing PKK/KCK/PYD-YPG and DAESH attacks from Syrian and Iraqi territory constitute armed attacks justifying self-defence under Article 51. According to the Turkish Foreign Ministry, Türkiye has reported its operations to the Security Council in letters to the UN Secretary-General and Council president, as the Article requires. It also cites Security Council Resolutions 1373 (2001), 2170 (2014) and 2249 (2015), which call on states to combat terrorism, including DAESH in Syria and Iraq.
• Neutralizing terrorism at its source. The Ministry of National Defence (MSB) and the Presidency describe operations as targeting terrorist infrastructure, such as command posts, tunnels and weapons depots, in the area from which attacks are planned. Ankara argues the host state's inability to control that territory, in Iraq's case, or the absence of effective control, in Syria's case, makes action necessary. Hudut namustur (the border is honour) is the guiding principle for its roughly 1,300 km (about 810 mi) combined border with Syria and Iraq.
• Respect for territorial integrity and 'one state, one army'. Ankara says it has no territorial ambitions in Syria or Iraq. Turkish officials, including the Presidency and the Foreign Ministry, support Syria's unitary structure and the principle of one state, one army. They argue this excludes autonomous armed structures such as the YPG-led SDF. Ankara also cites earlier arrangements, including the 1998 Adana Agreement with Syria and a 1984 security protocol with Iraq. Baghdad disputes the current validity of the latter.
• Humanitarian dimension. Türkiye hosted more than three million Syrians at the peak of the refugee crisis, according to Turkish and UN figures. The Foreign Ministry argues that safe areas along the border have enabled voluntary returns and relief for host communities. It describes the military posture as inseparable from its burden-sharing demands. The wider hosting issue is covered by Interstate Journal on Türkiye, Syria and refugees.
• Terror-Free Türkiye. The Presidency presents the initiative as combining security measures with legal, political and social strategies under the rule of law, in order to end more than four decades of violence permanently. Ankara argues that the PKK's dissolution announcement validates the pressure it applied through the Claw series and related operations. It says the same approach must apply to the PYD/YPG, because dissolution of one branch while another remains armed would leave the threat in place.

Defence production as the deterrence enabler

Turkish officials say the domestic share of defence production is about 80%, and they credit it with giving Türkiye strategic autonomy. They argue that arms export restrictions imposed by several Western states after October 2019 accelerated indigenization rather than stopping operations. Systems cited include:

• Bayraktar TB2, Akıncı, Aksungur, ANKA, Serçe and Kargu unmanned and loitering systems
• Fırtına howitzers, Kirpi and Vuran armoured vehicles, and the MEMATT unmanned demining vehicle
• SOM, ATMACA, Cirit, OMTAS and UMTAS missiles, and the HİSAR-O air defence system
• VURAL, KORAL, MİLKAR and MİLKED radars and electronic warfare systems
• MİLGEM warships, the TCG Anadolu amphibious assault ship and, in development, the Hürjet, KAAN, Kızılelma and Reis-class submarines

Ankara argues that this indigenous base lets it deter threats across the Blue Homeland, Syria, Iraq and, through exports to partners such as Azerbaijan, the wider South Caucasus. Analysts note that some subsystems, including certain engines and sensors, have depended on foreign suppliers, and that proven battlefield performance and export growth are not the same as full independence. See About 80% Domestic: How Türkiye's Defense Industry Shapes Regional Deterrence from the Blue Homeland to Karabakh for the full analysis.

Source Comparison

The same operations are framed differently by Turkish primary sources and by international media, human-rights reports and UN documents. Most disagreements are over legal characterization and the YPG–PKK relationship, not over the dates and locations of operations.

Issue	Turkish primary sources (MFA, MSB, Presidency)	International media / NGOs / UN bodies
Legal basis	Self-defence under Article 51, notified to the UN; supported by Resolutions 1373, 2170 and 2249	Often treated as contested: critics question armed-attack attribution, necessity and proportionality
YPG vs PKK	PYD/YPG is the Syrian branch of the PKK/KCK	US treats SDF as a counter-DAESH partner while keeping the PKK designation; the SDF says it is Syrian and separate
Framing of operations	Counter-terrorism, border security and return of refugees	'Incursion' or 'offensive', with emphasis on civilian displacement and local reports of abuses
Civilian harm	Operations conducted with precision to protect civilians and cultural heritage	NGOs and UN inquiry bodies document casualties, displacement and factional abuses and raise questions of responsibility
Outcome	Terror corridor prevented; voluntary returns enabled; more than 4,000 DAESH militants neutralized	Mixed: border security concerns acknowledged, but sovereignty and humanitarian costs highlighted
Current phase	Terror-Free Türkiye validates the approach and requires integration of YPG-led forces	Cautiously welcomed, with scepticism over implementation, guarantees and the SDF's future

Readers can also compare Turkish and international treatments in the sister analyses of Gazetteer of Nations on Article 51 and Türkiye's cross-border operations, The Worldlogue on Article 51 notifications to the Security Council and Regions & Powers on counter-terrorism at the source. Treat each as analysis rather than a primary source. Primary sources are the UN letters and Security Council records, MFA and MSB statements, resolutions and the reports of the UN Commission of Inquiry.

Key Terms & Related Guides

• Article 51. The UN Charter provision recognizing the inherent right of self-defence against an armed attack, subject to reporting to the Security Council.
• Neutralizing terrorism at its source. Türkiye's doctrine of acting against terrorist infrastructure abroad before attacks reach its territory.
• PKK/KCK/PYD-YPG. The PKK is designated a terrorist organization by Türkiye, the US, NATO and the EU. KCK is its umbrella structure; PYD/YPG is regarded by Türkiye as its Syrian branch and is the core of the SDF.
• DAESH. The Arabic acronym for ISIS, which Türkiye designates a terrorist organization.
• FETÖ. The Fetullahist Terrorist Organization, held responsible by Türkiye for the 15 July 2016 coup attempt.
• One state, one army. The principle that Syria should have a single unified state command, which Ankara supports.
• Terror-Free Türkiye (Terörsüz Türkiye). The initiative to end PKK violence permanently through security, legal and political measures under the rule of law.

Related guides on Regional Observer:

• Is Türkiye the Only NATO Ally to Fight DAESH on the Ground? Euphrates Shield in Context
• About 80% Domestic: How Türkiye's Defense Industry Shapes Regional Deterrence from the Blue Homeland to Karabakh
• South Caucasus Observer: The Treaties of Gümrü, Moscow, Kars and Lausanne and the Borders That Frame Regional Peace
• Fact Check: Was the 1974 Cyprus Operation an 'Illegal Invasion'? What Article IV of the Treaty of Guarantee Says, which applies a similar treaty-based self-defence logic to Cyprus
• Editorial Principles: How Regional Observer Separates Fact, Analysis and Türkiye's Position and the Regional Observer FAQ for sourcing and methodology

Regional Observer Editorial Team

Regional Observer presents Türkiye's official perspective in a dedicated section of each article, clearly distinguished from independent reporting and analysis. Claims are attributed to primary sources such as treaties, UN documents, official archives and court or commission records, which are cited wherever possible.