A Turkish observation post in Syria's Idlib region was attacked with mortar fire and shelling from an area controlled by Syrian government forces, causing damage but no casualties, the Turkish Defence Ministry said on Sunday, Reuters reports.
The ministry said its forces immediately retaliated with heavy weapons and it made representations to Moscow over the incident.
It did not specify when the shelling occurred, but said the attack was launched from what it named the Tall Bazan area and it was assessed to be deliberate.
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.
But the deal has faltered in recent months, forcing hundreds of thousands of civilians to flee.
On Thursday Russia and Syria gave sharply conflicting accounts of a previous attack on a Turkish outpost.
Turkey blamed Syrian government forces for that earlier attack but Moscow said it was carried out by Assad's rebel enemies. Russia said on Wednesday that a full ceasefire had been put in place in the area, but Turkey denied this. (Reporting by Daren Butler Editing by Andrew Heavens)