Kurdish separatist rebels killed at least seven Turkish soldiers when they opened fire on a military outpost in eastern Turkey, officials say.
A rebel also died in Monday's attack in Pulumur, a town in the Tunceli area, the Turkish security sources said.
The rebels drove a vehicle into the base and detonated a grenade. Seven soldiers were also injured.
The raid was blamed on the banned Kurdistan Workers Party (PKK), which has been active in Tunceli before.
The attack comes amid speculation Turkey may launch an incursion into Iraq to tackle Kurdish rebels following recent rebel operations inside Turkey.
On Monday Foreign Minister Abdullah Gul told EU officials Turkey had "every right" to take action against the rebels.
The latest violence is bound to fuel support for a military operation into northern Iraq, says the BBC's Sarah Rainsford, in Istanbul.
The government has already said it would approve such an incursion if the military requested it, she says.
Tunceli has long been known as a hotspot for PKK rebels
Turkey blames the PKK for a recent suicide bombing in Ankara and a landmine attack on troops.
The PKK has been fighting for an ethnic homeland since 1984. Turkey blames the group for 30,000 deaths since then.
Kurdish sources say Turkish troops on Sunday shelled an area just inside northern Iraq, near the border. No casualties were reported.
In the past Turkish forces have launched some cross-border raids to flush out PKK rebels.
Turkey has urged US and Iraqi forces to crack down on the PKK bases in northern Iraq.
Turkish officials are preparing to deliver a report to the UN calling for more co-operation against the PKK, a group the US and EU brand as terrorists.