Syrian rebels backed by the Turkish military said on Thursday they had recaptured the strategic town of Saraqeb in what would be the first major reverse for the Assad forces in a Russian-backed offensive that had made swift gains.
Three weeks ago, the armed opposition lost the northwestern town at the junction of two main highways, following advances by the regime forces in its push to retake the last large, rebel-held region in Syria after nine years of war.
Turkey has sent thousands of troops and heavy military hardware into Syria's Idlib region in an unprecedented incursion to back the rebels against the offensive by Assad forces.
Nearly a million Syrians have fled over the last three months, the biggest exodus of the war.
"The city of Saraqeb has been liberated completely from Assad's gangs," said Naji Mustafa, spokesman for a Turkish-backed coalition of rebel factions, the National Liberation Front.
With Russian backing, regime forces aided by Iranian militias have gained ground in northwest Syria since December.
Government forces have seized about 60 towns and villages in southern Idlib and the adjoining province of Hama in the last three days, the Syrian Observatory for Human Rights said.
Rebels said heavy fighting was still raging in an area that the army, backed by Iranian-militias, had controlled in fresh advances which the war monitor said had secured for the pro-government forces control of all of southern Idlib.
Opposition sources said a counter offensive was underway.
The push on Saraqeb comes ahead of an end-February deadline set by Turkish President Recep Tayyip Erdoğan for Assad's forces to pull back from territory that Ankara says is part of a buffer zone agreed with Russia.
Erdoğan has said Turkey would otherwise drive them back and the spokesman of his AK Party, Ömer Celik, said on Thursday preparations were complete.
"When the time given to the regime to withdraw expires, the Turkish Armed Forces will carry out their duties based on the orders they receive and nobody should doubt our determination about this," Çelik said.
Two Turkish soldiers were martyred in an air strike in Idlib on Wednesday, bringing Turkish forces' deaths in the region to 18.
As well as sending troops and military hardware into the region across its border, Ankara has set up new outposts in what rebels say is preparation for a Turkish operation.
Turkey, which has already taken in 3.6 million Syrian refugees, says it cannot handle another influx and has closed the border. Some migrants have made homes along the border wall, using it to prop up tents and shelters.
Ibrahim al-Idlibi, an opposition figure in touch with the rebel factions, said Saraqeb's seizure eases pressure on rebels, who in recent days lost significant territory in southern Idlib province and Jabal al Zawiya highlands.
Saraqeb is at the junction of two main roads linking the capital of Damascus, Syria's second largest city Aleppo and another highway west to the Mediterranean.
Taking back the M5 highway, which goes south to Damascus, had marked a big gain for Assad's forces as they restored state control over the route between Syria's two biggest cities for the first time in years of conflict.
Opening major highways in rebel hands to revive a shattered war economy has been a major goal of the Russian-led campaign.
"The opposition have now cut the highways and brought the regime to square one," said Syrian opposition defector general Ahmad Rahhal.
