Army helicopters later bombed PKK militants who carried out the attack in mountainous Tunceli province, the sources said.
One soldier was in critical condition, they said. Fighting continued and the army had sent more troops to the area, reported Worldbulletin.
Turkey's parliament on Wednesday extended for another year a mandate for the military to launch operations against PKK militants based in northern Iraq.
PKK killed 17 Turkish soldiers on a military outpost in the southeastern province of Hakkari days ago.