Damascus, Feb 7 (IANS): Syrian army troops besieged four Turkish observation posts as they pushed deep into a strategic rebel-held area in the war-torn country's northwestern region.

A Syrian military official told Efe news on Thursday that the forces backed by Russian planes were preparing to enter Saraqeb town in the eastern Idlib province after surrounding it.

The forces are now 7 km away from Idlib, the country's last rebel stronghold, according to the source.

The strategically important town, Saraqeb, lies on two major highways, one linking Damascus to Syria's second-largest city in the north, Aleppo, a main artery for government forces, and another connecting the country's west and east.

Turkey and Russia signed a deal in 2018 to establish a demilitarized zone with observation points manned by their respective troops in a bid to ease tensions in the provinces of Idlib, Hama, Latakia and Aleppo.

A total of four out of the 12 Turkish observation posts in the region are located in Idlib and its surroundings.

Idlib and western Aleppo are mainly under the control of former Al Qaeda affiliate Hayat Tahrir al-Sham, which has been ruled a terrorist group by Damascus and Moscow.

Tensions between Syria and Turkey flared up on Monday after Syrian forces carried out an attack that left eight Turkish victims dead, including five soldiers.

Turkish President Recep Tayyip Erdogan gave Syria an ultimatum until the end of February to pull military units out of areas close to Turkish army observation posts in Idlib.

On Wednesday, Erdogan warned that "if the (Syrian) regime does not withdraw in February, Turkey will be forced to take actions on its own".

Last month, Syrian government forces backed by Russian planes captured Maaret al-Nouman in Idlib, which had been under the control of insurgents since 2012.

The army offensive is taking place despite a ceasefire agreed by Russia and Turkey in Idlib earlier January.

Moscow is an ally of Syrian President Bashar al-Assad, while Ankara supports some rebel groups.