The cross-border ground operation was the first of its kind in two years against rebels from the outlawed Kurdistan Workers' Party (PKK) who use northern Iraq as a launching pad for attacks against targets inside Turkey.

Wednesday's incursion followed an attack by PKK rebels on border guards in the province of Sirnak which lies on the Iraqi frontier at 1:00 a.m. (2200 GMT), the statement on the military's website said.

A Turkish soldier was killed in subsequent fighting that lasted until the morning in which helicopter gunships backed Turkish forces.

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" (1.2 to 1.8 miles) inside Iraqi territory, the army statement said.

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

Turkish fighter jets also bombed a group of rebels as well as mortar and anti-aircraft gun positions detected deeper inside Iraqi territory, it said.

The targets were hit successully, the statement added.

The PKK, listed as a terrorist organisation by Ankara and much of the international community, has recently stepped up attacks against the security forces in Turkey's mainly Kurdish southeast.

The Turkish army has staged a series of air raids against PKK bases in northern Iraq since December 2007, often with the help of US intelligence, and in February 2008 carried out a week-long ground incursion.

Some 45,000 people have been killed in the conflict since 1984 when the PKK, took up arms against Ankara for self-rule in Turkey's mainly Kurdish southeast.