Three Turkish soldiers were killed in an explosion in southeastern Turkey blamed on PKK militants, a provincial governor's office said on Sunday.
The death toll rose to three after one soldier wounded in the blast late on Saturday died at a military hospital on Sunday morning, security sources said on condition of anonymity. The two others died at the scene.
Earlier, security officials said the soldiers, who were specialist sergeants, were killed during a firefight with PKK militants near the town of Nusaybin close to the Syrian border.
But a written statement from the governorate in Mardin province later said the officers died when a remote-controlled explosive detonated while they were on foot patrol.
An operation was ongoing to apprehend those behind the attack, the source said.
More than 40,000 people have died in the 26-year conflict. Some 100 military personnel have been killed so far this year, already exceeding last year's death toll.
Turkey has launched several cross border operations into the north of Iraq in the past to track down PKK militants, who took refuge at the their mountain camps there. The militant group uses the region as a launchpad for its attacks inside Turkey.
Turkey's government is under pressure to clamp down on violence ahead of parliamentary elections due in July 2011.