A Turkish security source emphasised they were only to reinforce the 12 existing posts established under a 2018 deal with Russia to prevent an offensive by Syrian government forces.

Hundreds of thousands of people have been forced to flee their homes in recent weeks as the Syrian regime, backed by Russian air strikes, presses an assault to retake Idlib.

Five Turkish soldiers and three civilians were killed earlier this week by regime shelling. Retaliatory fire by Turkey killed at least 13 Syrian troops.

Turkey says three of its outposts -- all in the southeastern part of the region -- have now been encircled by regime forces.

The UK-based Syrian Observatory of Human Rights monitor said Wednesday that Turkish troops at another position in Saraqeb had shelled Syrian forces to prevent it also being surrounded.

The security source refused to confirm those clashes but said Turkish forces in the area "are taking every kind of measure and will take every kind of measure" to ensure safety.

He said Turkey's priority was to stop the Syrian advance and reinstate the ceasefire, stressing that no Turkish soldiers would be evacuated.

Turkey and Russia have worked closely in recent years to resolve the situation in Idlib despite being on opposing sides of the conflict.

The Turkish source insisted that coordination with Russia remained strong and that joint patrols in northeastern Syria were only cancelled earlier this week due to "heavy weather conditions".

A delegation from Russia is expected in Turkey on Saturday for further talks, Turkish Foreign Minister Mevlut Cavusoglu told reporters in Ankara.