Clashes erupted at Mount Gabar, in Sirnak province, in a military operation against rebels from the Kurdistan Workers' Party (PKK), the sources said.

The NTV news channel said there were heavy losses on the PKK side, but gave no figures.

Turkey has massed an estimated 100,000 troops on the border amid threats of cross-border military strikes against PKK bases in northern Iraq where it says the rebels enjoy a safe haven.

Pressure for a cross-border operation increased after October 21 when PKK rebels carried out a deadly ambush on a Turkish military unit near the Iraqi border, killing 12 troops, injuring 17 and capturing eight.

Last week, US President George W. Bush pledged to provide Turkey with real time intelligence to strike at the PKK after talks with Turkish Prime Minister Recep Tayyip Erdogan in Washington.

A Kurdish official in northern Iraq told AFP that Turkish warplanes on Tuesday bombed three Iraqi villages near the border town of Zakho known to be frequented by PKK rebels. There were no casualties.

More than 37,000 people have been killed since 1984 when the PKK, blacklisted as a terrorist group by much of the international community, took up arms for self-rule in Turkey's mainly Kurdish southeast.