Reports from Syria say the army and pro-government militia are pushing into the town of Jisr al-Shughour in the north-west of the country.
Witnesses reported an attack using tanks and helicopter gunships after an early morning bombardment reports the BBC.
The government says it is trying to restore order after it claimed 120 security personnel had been killed.
But residents say the dead were killed after a mutiny and fighting between the security forces.
Tent city
The government advance sent more people fleeing towards the Turkish border.
Turkey says at least 4300 people have now fled the fighting in Syria to seek refuge across the border.
But a BBC correspondent on the border says the real number of displaced people is probably much higher.
Senior Foreign Ministry official Halit Cevik said Turkey would deal with the crisis as best it could.
''If they are coming, this is a humanitarian issue,'' he said. ''We will do whatever is needed within our means.''
He added that while Turkey could cope with the crisis at the moment, it might need international help if things got worse.
However, the BBC reports that Mr Cevik said that the UN refugee agency would not be involved.
The Syrians involved were not seeking refuge in Turkey, he said, as their eventual aim was to go back home.
