Two police officers have been killed in Turkey's predominantly Kurdish southeast during operations to push back Kurdistan Workers Party (PKK) militants, the Dogan news agency said on Friday.

The first policeman was killed in the district of Cizre late on Thursday when he and a group of colleagues came under rocket attack as they tried to break down barricades set up by PKK fighters, Dogan said.

Southeastern Turkey has plunged back into some of its worst violence since the 1990s after a two-year ceasefire between the PKK and the state collapsed in July.

The PKK first took up arms in 1984 to push for greater autonomy in the southeast and some 40,000 people have since been killed in the violence. It is designated a terrorist group by Turkey, the United States and European Union.

President Tayyip Erdogan said on Thursday there would be no let-up in a military campaign which he said had killed more than 3,000 militants this year in some of the heaviest fighting since their insurgency began three decades ago.