Four Turkish soldiers were killed Monday by Syrian regime shelling in the northwestern region of Idlib, Turkey's defence ministry said.
Nine other soldiers were wounded, including one seriously, the ministry said in a statement, adding that Turkish forces retaliated and "destroyed targets".
The ministry said the soldiers came under attack despite previous coordination on where they would be in the region.
It added Turkey was following the latest developments closely and that the necessary measures would be taken.
Turkey has 12 observation posts in the region as part of a Turkey-Russia deal to prevent a regime offensive.
The deaths come after local media reported Sunday that Turkey's military sent reinforcements to the region to bolster the forces stationed at the posts.
The Syrian regime, supported by Russian air strikes, has intensified its assault in recent weeks against Idlib, the last major opposition bastion.
Turkish President Recep Tayyip Erdogan last week warned Ankara could use "military force" against Syria as he hit out against the "cruelty" of the Damascus regime.
Turkey, which is home to over 3.5 million Syrian refugees, fears another influx from renewed violence in Idlib.
Hundreds of thousands of people have already been displaced in the region, while many of them have fled towards the Turkey-Syria border.
Erdogan previously said Turkey was building homes on the Syrian side of the border to shelter those fleeing.
Turkey has 12 observation posts in the northwestern region of Idlib as part of a Turkey-Russia deal to prevent a regime offensive