Turkish fighter jets have bombarded Kurdistan Workers’ party (PKK) positions in south-eastern Turkey for the first time since the start of the peace process between the outlawed group and the Turkish government in 2012.

The attacks on the PKK came in the wake of violent clashes last week between Kurdish factions and security forces in several Turkish cities, as anger grows over perceived government inaction against the Islamic State (Isis) attack on the Kurdish town of Kobani in Syria.

According to media reports, Monday’s strikes came in retaliation for armed PKK offensives on several military outposts in the area. The reports claim that the targeted PKK units had been attacking Dağlıca military posts using rocket-propelled grenades and small-arms fire for three days.

The Turkish chief of general staff said the military “opened fire immediately in retaliation, in the strongest terms” after repeated PKK attacks in the area, and before air strikes were launched.

The Turkish daily Hürriyetreported that the air strikes caused “major damage” to the PKK, while the Kurdish Firat news agency said there had not yet been any confirmation of casualties and losses on the rebel side.

The People’s Defence Force (HPG), the armed wing of the PKK, confirmed several air strikes in Hakkari province. “After almost two years the occupying Turkish army conducted a military operation against our forces yesterday for the first time […] with these air strikes they violated the ceasefire,” a statement read.

Other Turkish newspapers also reported armed clashes between the PKK and troops in the Tunceli area of east-central Turkey on Monday.

Meanwhile, Syrian Kurds in Kobani rejected claims by Iraq’s Kurdistan regional government that military aid had secretly been delivered to forces battling Isis. “We have not received any military aid from anyone so far,” said Idris Nassan, deputy foreign minister of the Kobani administration. “We would have made such aid public for sure.”

A number of those killed died in clashes between PKK supporters and members of the Free Cause party (Hüda Par), thought to be linked to Hezbollah, a Sunni militant group from Turkey that gained notoriety in the 1990s when it was recruited by the Turkish “deep state” to murder and torture hundreds of PKK members and supporters in the region. Hüda Par leaders rejected all responsibility for the violence last week and accused PKK members of deliberate provocation and political exploitation of the situation in Kobani.

Observers fear that tensions between the PKK and their Sunni Islamist rivals might stir wider unrest and derail the Turkish peace process. The air strikes are the first major mutual break of the ceasefire since the peace process was launched in 2012 as an effort to end a bloody conflict that has killed more than 40,000 people in 30 years.