Turkey announced early Sunday that it had conducted airstrikes against banned Kurdish militant bases in northern Syria and Iraq, which it said were being used to launch “terrorist” attacks on its soil.

The offensive, codenamed Operation Claw-Sword, comes after a deadly blast in central Istanbul last Sunday that killed six and wounded 81, with Turkey blaming a banned Kurdish group.

“We begin Operation Claw-Sword from now on,” Defense Minister Hulusi Akar said at the Air Force Operations Center before the planes left their bases to hit targets in northern Iraq and Syria.

Akar was also featured in a video image briefing President Recep Tayyip Erdogan, who gave the order for the latest operation that killed 12 people, according to a monitor.

The raids targeted bases of the banned Kurdistan Workers’ Party (PKK) and the Kurdish People’s Protection Units (YPG), which Ankara sees as an extension of the PKK, the defense ministry said.

“In accordance with our self-defense rights under Article 51 of the United Nations Charter, the Claw-Sword airborne operation was conducted in the regions of northern Iraq and Syria used by terrorists as bases for attacks on our country. ‘ it added.

Turkey blamed the PKK for the Istanbul bombing, the deadliest in five years, which revived bitter memories of a 2015-17 wave of nationwide bombings that were mostly attributed to Kurdish militants and jihadists from the Islamic State group.

The PKK, which has been waging a bloody insurgency in Turkey for decades and labeled a terrorist group by Turkey and its western allies, and the YPG have both denied any involvement in the attack.

No individual or group took responsibility.

Turkish police have arrested prime suspect Alham Albashir – a Syrian woman believed to have worked for Kurdish fighters – in a suburb of Istanbul.

“The hour of reckoning has come,” Turkey’s Defense Ministry tweeted, along with a photo of a plane taking off on a night mission.

“The insidious attacks of the villains will be held accountable,” it said.

“Terrorist hotbeds destroyed by precision strikes,” the ministry said in another post, which was accompanied by video showing a target being selected from the air, followed by an explosion.

Turkey has carried out more than 20 attacks on sites in Syria’s Raqa, Aleppo and Hassakeh provinces, said the Syrian Observatory for Human Rights, a UK-based monitoring group that has an extensive network of contacts across Syria.

At least six members of the Kurdish-led Syrian Democratic Forces (SDF) and six soldiers loyal to the regime were killed in the raids, the observer said.

A PKK spokesman said the strikes had not claimed any casualties so far.

The Turkish army regularly attacks the PKK’s rear bases in Iraq – a thorn in Ankara’s relations with the Baghdad government – and has been conducting Operation Claw-Lock in northern Iraq since April in a bid to pursue militants.

While Ankara did not provide details of the operation, the US-backed SDF said the city of Kobane in northeastern Syria was among the targets of the Turkish raids.

“#Kobane, the city that defeated ISIS, is being bombed by Turkish occupation planes,” tweeted Farhad Shami, a spokesman for the SDF.

The SDF provided crucial assistance to a US-led coalition against jihadists from the Islamic State (IS) group.

However, Turkey regards the YPG as a terrorist group linked to the PKK.

Turkey’s Interior Minister Suleyman Soylu said Ankara believes the order for the attack in Istanbul was issued from Kobane, which is controlled by Syrian Kurdish militias.

“Turkish bombing raids on our safe areas threaten the entire region,” tweeted Mazloum Abdi, commander in chief of the US-allied SDF.

“This bombing is not in favor of any party. We make every effort to avoid a major disaster. If war breaks out, everyone will be affected.”

Kobane, a Kurdish-majority town near the Turkish border, was captured by IS in late 2014 before Syrian Kurdish forces expelled it early the following year.

The US State Department said on Friday it feared possible military action by Turkey and advised its nationals not to travel to northern Syria and Iraq.

Turkey has launched waves of attacks on Syria since 2016, targeting both Kurdish militias and IS jihadists, and Ankara and its-backed forces have seized areas along the Syrian border.

Erdogan has been threatening a new operation in northern Syria since May.