Five police officers were killed and four others were wounded when a car bomb exploded as a police vehicle passed in southeastern Turkey on Monday in an attack that appeared to have been carried out by Kurdish militants, security sources said.

Yavuz Selim Koser, the governor for Bingol, said four other police officers were seriously wounded in Monday’s attack in the mainly Kurdish province. He blamed the attack on the Kurdistan Workers’ Party, or PKK, which has been fighting Turkey for Kurdish autonomy since 1984.

Members of the outlawed Kurdistan Workers Party (PKK) carried out the attack in Bingol province, the sources said. Two of those injured were in serious condition.

The PKK, listed as a terrorist organization by Turkey, the United States and European Union, has waged an armed campaign against security forces in the mainly Kurdish southeast since 1984, pushing for Kurdish autonomy. More than 40,000 people, have died in the violence.

Unrest has flared anew since a ceasefire collapsed in July 2015, and thousands of militants and hundreds of soldiers and police have since died. Rights groups have said about 400 civilians have also perished.

Clashes between the PKK and the Turkish security forces resumed a year ago after a fragile peace process collapsed. The renewed conflict has led to the death of nearly 600 security personnel and more than 5,000 Kurdish militants.

Last week, eight Turkish soldiers and 35 Kurdish militants were killed in clashes in the southeastern province of Hakkari.