The fighting erupted early Thursday in the mountains between Pulumur and Nizamiye in the province of Tunceli, where a security operation against the separatist Kurdistan Workers' Party (PKK) had been under way for the past two days, the sources said.

The operation is continuing with air cover, the Anatolia news agency reported.

Turkey stepped up action against the PKK from December and conducted several air strikes and a week-long ground incursion into northern Iraq, where it says more than 2,000 PKK rebels take refuge.

The PKK, listed as a terrorist group by Turkey and much of the international community, has been fighting for self-rule in the mainly Kurdish southeast since 1984. The conflict has claimed more than 37,000 lives.