Syrian regime forces re-entered the northwestern town of Saraqeb on Monday after losing it days earlier to opposition fighters, the Syrian Observatory for Human Rights and state media said.
"Regime forces with Russian air cover were able to retake complete control of the town of Saraqeb on the Damascus-Aleppo highway," the war monitor said.
Syrian state news agency SANA said the army had re-entered the town after violent clashes with Turkey-backed fighters.
Opposition spokesman Naji Mustafa, however, said regime leader Bashar al-Assad's forces had only taken part of the ghost town long emptied of its inhabitants.
"Assad's forces have launched an assault on Saraqeb and very violent clashes are ongoing inside," the spokesman for the National Liberation Front said.
Pro-government forces for the first time in years wrested control of the town on February 8, but militants and allied fighters then re-entered on Thursday.
Since December, Russia-backed regime forces have led a deadly military offensive against the last major opposition stronghold of Idlib, where Turkey supports some opposition groups.
The assault has caused almost a million people to flee their homes and shelters in the middle of winter.
The Observatory said Damascus deployed regime troops and allied fighters from Lebanon's Hezbollah as reinforcements to the Saraqeb area late Sunday in preparation for an assault on the town.
Up to 23 rebels and extremists were killed in Russian airstrikes and clashes overnight, Observatory chief Rami Abdel Rahman said.
Violence has escalated between regime fighters and Turkish forces in the Idlib region in the past weeks, killing dozens of troops on each side.
On Sunday, Turkey confirmed a full military operation in northwest Syria after a Thursday airstrike blamed on Damascus killed 34 Turkish soldiers.
The Observatory says more than 90 regime soldiers have been killed in Turkish bombardment since Friday, as have 10 Hezbollah fighters.
Saraqeb is a strategic prize for the Syrian regime.
The town lies at the intersection of the M5 and M4 highways, which connect the capital and regime coastal stronghold Latakia with second city Aleppo respectively.
On Sunday, SANA reported that the government shot down a Turkish drone near Saraqeb, publishing footage of an aircraft tumbling from the sky in flames.
Turkish President Recep Tayyip Erdogan and his Russian counterpart Vladimir Putin, whose support for Assad turned the tide of the war five years ago, are due to meet in Russia on Thursday to seek agreement on Idlib.