Rebel spokesman Ahmad Denis said Turkish troops had penetrated two kilometres (more than a miles) across the border in the Haft Tanin area of Dohuk province, one of three that make up the autonomous Kurdish region of northern Iraq.

"Heavy clashes are continuing on the border," Denis told AFP.

"We haven't counted our losses yet, we will announce them later. We inflicted huge losses on the Turkish army."

The spokesman confirmed that the ground troops were backed by helicopter gunships but denied the Turkish army's report that fighter jets also bombed a group of rebels and mortar and anti-aircraft gun positions deeper inside Iraqi territory.

Denis had initially denied that there was any ground incursion or PKK losses either.

It was Turkey's first ground operation over the border in two years and followed an upsurge in fighting since the rebels announced on June 4 that they were ending a unilateral truce.

Overnight, PKK fighters attacked border guards in neighbouring Sirnak province and killed a Turkish soldier in fighting that lasted until the morning, the Turkish army said.

When the rebels fled into northern Iraq, a company of commandos and special forces units followed in pursuit.

"Four terrorists were killed in clashes at the border and two to three kilometres" (between one and two miles) inside Iraqi territory, the army added.

The Turkish soldiers "are still continuing a sweep of the region."

The PKK has long used rear-bases in northern Iraq to press its quarter-century armed campaign for Kurdish self-rule in eastern Turkey.