The fighting broke out near the town of Silvan and was still ongoing at 1500 GMT. It also left six soldiers wounded, two of them seriously.

It was not immediately clear how many lives the fighting had claimed in the ranks of the Kurdistan Workers' Party (PKK).

The fierce clashes started a fire in a nearby forest, the sources said.

According to the Anatolia new agency, Prime Minister Recep Tayyip Erdogan cancelled his engagements in Istanbul to convene an emergency meeting with the country's top security chiefs.

A Turkish soldier was killed and three were wounded in clashes with the PKK last week in the eastern Pulumur area.

The PKK, listed as a terrorist group by Turkey and much of the international community, took up arms in 1984, sparking a conflict that has claimed some 45,000 lives.

In February, the rebels threatened to end a unilateral truce, declared in August last year, while saying they would defend themselves "more effectively" against military operations.