One Turkish soldier was killed and three others were wounded on Thursday when their observation post in Syria's Idlib region was attacked by shelling and mortar fire, the Turkish Defense Ministry said.
The attacks were launched from territory controlled by Syrian government forces and were judged to have been carried out deliberately, the ministry said in a statement. The wounded were evacuated and they have begun to receive treatment, it added.
The ministry said Russia's Ankara attache was summoned to military headquarters in connection with the attack and was told that the attacks will be "punished in the strongest way".
Similar attacks were carried out on Turkish observation posts in the region earlier this month. After the previous attack, the Turkish military retaliated with heavy weapons.
Russia, which supports Syrian President Bashar al-Assad in his country's civil war, and Turkey, long a backer of rebels, co-sponsored a de-escalation agreement for the area that has been in place since last year.
The accord has faltered in recent months, forcing hundreds of thousands of civilians to flee. Idlib is the last remaining bastion for anti-government rebels after eight years of civil war.