Syrian troops were regrouping outside Idlib city on Sunday, a day after it became the second provincial capital to fall from regime control, a security source and media said.
"Forces are repositioning on the outskirts of Idlib in order to face the terrorist battalions... and be in the best position to repel their attack," a security source in Damascus told AFP.
The Al-Watan newspaper, which is close to the government, said that troops had carried out a "successful operation regrouping south of the city".
"Army reinforcements were sent to start a military operation to regain control of the areas that were vacated after the evacuation of the local population to safe areas," the daily added, citing a source on the ground.
Opposition forces including Al-Qaeda's Syrian affiliate Al-Nusra Front seized control of Idlib on Saturday, the fifth day of fighting for the northwestern city.
The capture made it just the second provincial capital to fall from regime control after the March 2013 takeover of Raqa city in northern Syria.
Raqa was captured by assorted rebel groups but was subsequently seized by the jihadist Islamic State group, which has made the city the de facto Syrian capital of its self-declared Islamic "caliphate".
With the loss of Idlib, regime forces are confined to only a few bastions in the northwestern province, including the cities of Jisr al-Shughur and Ariha, the Abu Duhur military airport and several military bases.
Al-Nusra and its Islamist allies wield significant control elsewhere in the province, after ousting a string of Western-backed rebel groups from the region last year.