The Turkish Armed Forces says three Turkish soldiers were killed and 10 were wounded in Syria by an airstrike allegedly fired by government forces.
A statement from the Armed Forces on its website says the attack took place before dawn on Thursday. The statement did not provide the location for the 3 a.m. strike.
One of the wounded soldiers was said to be in critical condition.
The casualties are likely to ratchet up tensions between Ankara and Damascus. In August, Ankara sent ground troops into northern Syria to support Syrian opposition forces in the fight against Islamic State militants and to curb Syrian Kurdish territorial gains.
The Turkish troops are not fighting Syrian government forces.
Ankara views Syrian Kurdish troops as an extension of the Kurdish insurgency in southeastern Turkey.