Television news channels showed helicopters firing on rebel positions in the mountains near the town of Pervari in Siirt province in southeast Turkey.

Four fighter planes took off from the region's largest city of Diyarbakir, though their destination was unknown, said a Reuters witness.

Violence has risen in recent months and more than 50 Turkish soldiers have been killed as the Kurdistan Workers Party (PKK) increased attacks in the primarily Kurdish southeast.

The air and ground operation was launched in Siirt after rebels ambushed and killed two soldiers and three paramilitary village guards late on Wednesday, the army said.

"In a coordinated effort, 12 terrorists were killed and their weapons were confiscated by reinforcements sent to the region," the army said.

Turkish Prime Minister Tayyip Erdogan's initiative to expand Kurdish rights has floundered, and the government is facing public anger at its inability to stem the rising violence ahead of next year's elections.

The PKK called off a unilateral cease-fire on June 1.

Erdogan has called on allies in Europe and the Middle East to cut off the rebels' funds and extradite suspected militants.

Syrian security forces detained 400 people in an operation against the PKK, Turkey's state news agency said on Thursday.

The PKK also has bases in northern Iraq, where intelligence sharing between Turkey and the United States has led to sporadic Turkish air raids on the group.

Washington and the European Union, like Ankara, consider the PKK a 'terrorist organization'.

A lesser-known separatist agency killed six people in a bomb attack in Istanbul last week.

The PKK took up arms against Turkey in 1984 in a bid to carve out an independent Kurdish state. More than 40,000 people, mainly Kurds, have died in the war.

Violence traditionally rises in the southeast, which borders Iraq where most of the PKK is based, in the spring and summer months as warmer weather allows the rebels and the army to move more easily through the region's mountainous terrain.