Regime forces launched a fierce assault on the rebel bastion of Rastan in central Syria on Wednesday, raining shells on the town before launching a ground attack, a monitoring group and activists said.
There was no immediate word on possible casualties at Rastan but the Syrian Observatory for Human Rights said six people were killed Wednesday in other parts of violence-swept Syria.
The Observatory said Syrian troops were trying to infiltrate Rastan under the cover of heavy gunfire, shelling and rocket bombardment, adding that at one stage shells were falling at a rate of "one a minute."
An activist reached via Skype told AFP that rebels of the Free Syrian Army are defending the entrances of the town but that "regime forces are being strengthened with new deployments, including reinforcements from the revolutionary guard."
"The Free Syrian Army has total control over Rastan's entrances," said activist Abu Rawan.
"Electricity has been cut off in Rastan, and water tanks have been shelled," he said. "There is also a severe lack of food because the market is closed and we can't bring food in from nearby villages."
Besieged by regime forces, Rastan is home to a large number of rebel fighters, according to opposition sources.
Most of Rastan's residents have fled after months of fighting, but despite numerous assaults, regime forces have been unable to overrun the town.
The Observatory, meanwhile, said a civilian was shot dead near an army checkpoint at Inkhel in the southern province of Daraa.
In nearby Sheikh Meskin, several youths were arrested, according to the Britain-based watchdog.
Another civilian was killed by regime forces in the northern city of Aleppo, while in Qusayr in the central Homs province, a third civilian was shot dead by a sniper, the monitoring group added.
In the suburbs of Damascus, a blast killed three people on the international airport road, the Observatory said, without specifying whether they were civilians or soldiers.
A loud explosion was heard in the capital Damascus, the Observatory said, without providing any further details on the blast.
Other blasts were heard in several Syrian provinces during the night, including in Harasta and Douma, two suburbs of the capital that have seen fierce fighting between regime and rebel forces in the past few days.
A total of 26 people, including 14 civilians and 12 soldiers, were killed in violence on Tuesday, the Observatory said.
Fighting has grown increasingly violent around Damascus, Aleppo and northwest Idlib, despite the presence of some 270 UN truce monitors on the ground.
More than 12,000 people have been killed in Syria since a revolt broke out in March last year, prompting the regime to launch a fierce crackdown on dissent.