A car bomb and rocket attack killed two police officers and wounded 35 people in the southeastern Turkish province of Mardin on Friday, security sources say.

There was no immediate claim of responsibility for the 6 a.m. attack, but the security sources told Reuters the attack was carried out by Kurdistan Workers Party (PKK) militants in the town of Nusaybin, near the Syrian border, they said.

A ceasefire between the PKK and the state collapsed last July, and attacks on Turkey's security forces have since increased amid a surge in violence in the predominantly Kurdish southeast that has killed hundreds of people.

Violence has also increased elsewhere in Turkey.

On Thursday two female militants were killed by police when they fired shots and threw a grenade at a police bus in Istanbul. The attackers were identified as members of the leftist DHKP-C militant group, state-run Anadolu Agency reported. Two police officers were lightly wounded in the attack, Gov. Vasip Sahin told reporters in televised comments.

A suicide car bombing targeting military buses in Ankara killed 29 people last month. The government said that attack was carried out by a member of the Syrian Kurdish YPG militia with help from the PKK.

Turkey has also become a target for ISIS militants, who are blamed for three suicide bombings: one last year in the town of Suruc near the Syrian border, another in the capital, Ankara, and another in Istanbul in January. Those attacks killed more than 140 people.

The PKK, considered a terrorist group by Turkey, the United States and the European Union, launched a separatist armed rebellion against Turkey in 1984. More than 40,000 people, mostly Kurds, have since been killed.