Syrian troops attacked the town of Rastan with helicopter gunships on Monday, according to opposition activists.
The aerial assault follows several failed attempts by ground troops to seize the central town, the local co-ordination committees said.
Government shelling was also reported in Homs, Hama, Daraa, Aleppo, Deir el-Zour and even suburbs of Damascus as the country descends into civil war.
"The regime is now using helicopters more after its ground troops suffered major losses," said Rami Abdul-Rahman of the Britain-based Syrian Observatory for Human Rights.
Foreign Ministry spokesman Jihad Makdissi recently said rebels were using "sophisticated anti-tank missiles" against the government's ground forces.
Casualties from the attacks could not be confirmed but the Observatory said four civilians, one army defector and eight unidentified individuals had been killed in Deir el-Zour, while at least three people were killed in Hama.
British Foreign Secretary William Hague hinted on Sunday that a Western attack on the country was still possible, saying Syria "was on the edge of collapse or a sectarian civil war so I don't think we can rule anything out."
But Russia and China remain committed to a negotiated solution to the crisis.
The Russian Foreign Ministry denied that it was an "advocate" for the Bashar al-Assad government today but added: "We are speaking for the strict observance of the norms and principles of international law," which rule out attacks on sovereign states.
The Syrian government blames escalating violence on the rebels and alleges that they are being armed by the West.
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