The operation near Ovacik town in Tunceli province was launched after two Turkish soldiers and a militant from the outlawed Kurdistan Workers' Party (PKK) were killed in a clash there on Wednesday, the source added.

The fighting comes just two weeks after the PKK said it was extending a unilateral ceasefire with Turkey by one month to help establish "trust" with Ankara in its efforts to resolve a deadly 26-year Kurdish insurgency on its soil.

Since August last year, the Turkish government has been engaged in a cautious two-pronged strategy of keeping the PKK under military pressure and expanding the rights of its sizeable Kurdish population in the hope of persuading the rebels to lay down their weapons.

Blacklisted as a terrorist group by Ankara and much of the international community, the PKK picked up arms for self-rule in Turkey's mainly Kurdish southeast in 1984, sparking a conflict that has claimed some 45,000 lives.