There are reports that more than 200 people, mostly civilians, have been massacred in a Syrian army and militia onslaught on a village in the rebellious province of Hama.

If confirmed, it would be the worst single incident of violence in 16 months of conflict in which rebels are fighting to topple president Bashar al-Assad and diplomacy to halt the bloodshed has been stymied by deadlock between world powers.

The Revolution Leadership Council of Hama said the Sunni Muslim village of Taramseh was assaulted by helicopter gunships and tanks and that pro-government Alawite militiamen then stormed in and carried out execution-style killings.

"More than 220 people fell today in Taramseh. They died from bombardment by tanks and helicopters, artillery shelling and summary executions," the regional opposition group said in a statement.

Syrian state television said three security personnel had been killed in fighting in Taramseh and it accused "armed terrorist groups" of committing a massacre there.

Fadi Sameh, an opposition activist from Taramseh, said he had left the town before the reported killing spree but was in touch with residents.

"It appears that Alawite militiamen from surrounding villages descended on Taramseh after its rebel defenders pulled out, and started killing the people," he said.

"Whole houses have been destroyed and burned from the shelling. Every family in the town seems to have members killed. We have names of men, women and children from countless families," he added, saying many of the bodies were taken to a local mosque.

Ahmed, another local activist, said people we killed as the attempted to flee the onslaught.

"So far, we have 20 victims recorded with names and 60 bodies at a mosque. There are more bodies in the fields, bodies in the rivers and in houses... people were trying to flee from the time the shelling started and whole families were killed trying to escape," he said.

The reports could not be independently confirmed as Syrian authorities severely restrict the activities of independent journalists.

They are the latest in a series of attacks on civilians, including 78 people who were shot or stabbed dead or burned alive in the village of Mazraat al-Qubeir, a Sunni Muslim hamlet by members of Mr Assad's Alawite sect on June 6, and 108 men, women and children who were massacred in the town of Houla on May 25.

Most of Mr Assad's political and military establishment are members of the minority Alawite sect, an offshoot of Shiite Islam. The revolt and the fighters behind it are mostly Sunni Muslims.

While the insurgents have been unable to match the Syrian army's firepower, they have established footholds in towns, cities and villages across Syria, often prompting Mr Assad's forces to respond with helicopter gunships and artillery.

Reuters