A mass grave was found in Jisr Al Shughur on Sunday, Syria's official Sana news agency said, as state television reported battles with "armed gangs" in the flashpoint northern town.
"A mass grave was discovered in Jisr al-Shughur containing (the bodies of) security agents from the police headquarters" in the city, it said without specifying the number of bodies.
"Armed groups had mutilated the corpses which were removed from the mass grave," SANA added.
Jisr al-Shughur has been the focus of military operations since Friday, following what the authorities said was the massacre of 120 policemen by "armed gangs" in the town earlier in the week.
Syrian troops on Sunday battled with "armed gangs" in Jisr Al-Shughur and "army divisions... purged the state hospital of armed groups," state television reported.
Earlier, rights activists reported heavy gunfire and explosions in the northwestern town near the Turkish border after troops backed by helicopter gunships and around 200 tanks launched a two-pronged morning assault.
The rights activists told AFP by telephone the army fired barrages of shells into Jisr al-Shughur before entering the town, which they said was largely deserted after thousands had fled ahead of the crackdown.
Syria's Idlib province, where Jisr al-Shughur lies, has long been a hotbed of hostility towards the regime of President Bashar al-Assad.