Syrian troops regrouped on Sunday after a coalition including Al-Qaeda's local affiliate seized the city of Idlib, the second provincial capital to fall from government control.
The capture is a blow to the government and raises the prospect that Idlib will become the effective capital of territory held by Al-Qaeda's Syrian wing, Al-Nusra Front, analysts said.
On Sunday, the city in northwestern Syria was largely quiet, after sporadic government aerial bombardment overnight, the Britain-based Syrian Observatory for Human Rights monitor said.
A security source in Damascus and Syrian media said government forces were regrouping outside the city.
"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.
Al-Watan newspaper, which is close to the government, said 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.
A coalition of Islamist forces overran Idlib on Saturday, after an operation that began just five days earlier and killed at least 170 opposition and regime forces.
The city becomes only the second provincial capital to fall from regime control after Raqa, in northern Syria, which was seized by rebel groups in March 2013.
Those groups were subsequently ousted from the city by the Islamic State jihadist group, which has made Raqa the de facto Syrian capital of its self-declared Islamic "caliphate" on Syrian and Iraqi territory.
The group that seized Idlib calls itself the Army of Conquest and includes Al-Nusra and the powerful Islamist group Ahrar al-Sham, as well as other smaller conservative Islamist rebel forces.
Ahrar al-Sham, which lost 40 fighters according to the Observatory, issued a call for Idlib's victors "to put partisan interests aside" and "give a good image of Islam in administering" the city.
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The rebels touted their victory on social media, with Al-Nusra's Twitter accounts posting photos of its fighters in front of government buildings.
Al-Nusra also posted video of its forces entering a prison in the city, where they discovered the bodies of detainees apparently executed by government forces before their withdrawal.
The Observatory said at least 15 prisoners had been found dead at a military intelligence detention facility in the city.
- Opposition lauds city's fall -
The city's capture was praised by opposition forces across the spectrum of Syria's uprising, which began in March 2011 with anti-government protests before descending into a brutal war after a regime crackdown.
The opposition National Coalition, which is recognised by much of the international community, welcomed it as "an important victory on the road to the full liberation of Syrian territory".
Its statement made no reference to the composition of the forces that seized the city, saying only that it had "confidence" they would protect civilians and abide by international law.
Analysts said Al-Nusra's role in Idlib's capture had put the Coalition and other "moderate" rebels in a difficult position.
"The capture of Idlib is huge boost for the Syrian opposition, but it's one that once again will serve to underline the relative inadequacies of genuine 'moderates'," said Charles Lister, a visiting fellow at the Brookings Doha Centre think tank.
Al-Nusra and its allies already control a large portion of Idlib province, after a November offensive in which they ousted several Western-backed opposition groups.
And last year, the group announced plans to eventually establish an "emirate" that analysts say is intended to rival IS's "caliphate".
"Considering the posture established by Al-Nusra in Idlib over the last nine months, it seems pretty implausible that the city won't eventually end up representing Nusra's effective capital and stronghold," Lister said.
More than 215,000 people have been killed in Syria since the conflict began, and half the country's population has been displaced.