The soldiers were killed after the army killed a PKK suspect

It is one of the heaviest losses the Turkish military has sustained in clashes with the group. Reports say only one PKK fighter was killed.

The Turkish military shelled the border area in an attempt to prevent the fighters from fleeing to northern Iraq.

Ankara says about 3,000 PKK fighters are based in Kurdish-run north Iraq.

The Turkish government has been reluctant to push for a cross-border military operation but has repeatedly called on the US and the Iraqi authorities to take action against them.

"Those who create, feed and support terrorism should know that no force can stand against the determination of the Republic of Turkey to protect its inseparable integrity," Turkey's President Abdullah Gul said.

Constant clashes

"Thirteen members of our armed forces were killed in an attack ... carried out by terrorists on one of our units serving in the Sirnak region," a General Staff statement said.

The BBC's Sarah Rainsford says there have been almost constant clashes between Turkish forces and the PKK since thousands of troops were deployed in the border region earlier this year.

She says this latest ambush will increase military pressure on the Turkish government to send troops across the border.

Last month Iraq denied Turkey permission to pursue armed separatists onto Iraqi territory.

Instead Iraq and Turkey signed a wide-ranging security agreement, pledging to prevent finance, logistical support and propaganda for the PKK.

The PKK has been fighting for autonomy in south-eastern Turkey since 1984 and more than 30,000 people have been killed in the conflict.