Islamist insurgents including al-Qaeda's wing in Syria, Nusra Front, captured the northwestern Syrian town of Jisr al-Shughour on Saturday, for the first time in the four-year-old conflict.
Syrian state media said the army had redeployed to the town's surroundings "to avoid civilian casualties". They said the army was battling "a large number of terrorists coming from the Turkish border."
The capture of the strategic town is the latest in a series of setbacks for government forces in the south and the north.
Opposition fighters and the Syrian Observatory for Human Rights said the town, on a road between the coastal city of Latakia and city of Aleppo, was now fully controlled by insurgents
"All of Jisr al-Shughour is now liberated, there is no more regime there," Ahmad of the media office of the Islamist Ahrar al-Sham group, which is taking part in the battle, told Reuters.
After taking the town, fighters continued their assault with the aim of pushing the army from the few remaining government areas in the province of Idlib.
Last month the Sunni Islamist groups seized the city of Idlib, the capital of the province of Idlib near Turkey, after forming an alliance which includes Nusra, the hardline Ahrar al-Sham movement and Jund al-Aqsa, but not Islamic State, their rival.
The Islamist alliance calls itself Army of Fatah, a reference to the conquests that spread Islam across the Middle East from the seventh century.
Islamist groups agreed to unite in the battle for Jisr al-Shughour under the name "Battle for Victory". The formation of alliances by groups before major battles is one of the factors behind the advances, sources say.
By taking Jisr al-Shughour, the insurgents have edged closer to the coastal province of Latakia, Syrian President Bashar al-Assad's stronghold, and are now less than 8 km (five miles) from villages loyal to the government near the coast.
"Jisr al-Shughour is more important than Idlib itself, it is very close to the coastal area which is a regime area, the coast now is within our fire reach," Ahmad from Ahrar al-Sham said.
Syrian forces captured the town of Jisr al-Shughour in June 2011 when what the government described as armed gangs killed more than 120 security personnel in the town after large demonstrations there.
A rebellion in Jisr al-Shughour, a town of 50,000, in 1980 against President Hafez al-Assad, Bashar's father, was crushed with scores of deaths.