Syrian opposition activists accused President Bashar al-Assad's army Sunday of massacring scores of people in a town near Damascus that it recently recaptured from rebels.

Around 320 bodies, some of them women and children, were found in houses and basements around Daraya, according to activists who said most had been killed "execution-style" by troops during house-to-house raids, Reuters reported.

Activists uploaded several videos to the Internet showing rows of bloodied bodies wrapped in sheets. Most of the dead appeared to be young men of fighting age, but at least one video showed several children who appeared to have been shot in the head. The body of one toddler was soaked in blood. 

With independent media largely banned in Syris, it was impossible to verify the accounts.

"Assad's army has committed a massacre in Daraya," Abu Kinan, an activist there, told Reuters, using an alias to protect himself from reprisals.

The killings in Daraya, a working-class Sunni Muslim town that sustained three days of heavy bombardment before being overrun by the army on Friday, raised the daily death toll to 440 people on Saturday, one of the highest since the uprising started in March last year, said the Local Coordination Committees

Video footage from activists showed numerous bodies of young men side-by-side at the Abu Suleiman al-Darani mosque in Daraya, many with what looked like gunshot wounds to the head and chest.

"A massacre," said the voice of the man who appeared to be taking the footage. "You are seeing the revenge of Assad's forces ... more than 150 bodies on the floor of this mosque."

But the official Syrian Arab News Agency said: "Our heroic armed forces cleansed Daraya from remnants of armed terrorist groups who committed crimes against the sons of the town and scared them and sabotaged and destroyed public and private property."

Assad's forces launched an assault on Darayya on Saturday, after days of heavy bombardment, part of a drive to reclaim the southern outskirts of Damascus, where rebels have been regrouping since being driven out a month ago.

The British Foreign Office told the BBC it had opposition reports that "300 people, including women and children, were killed and that some were shot at close range".

Foreign Office Minister Alistair Burt said that, if confirmed, the killings would require "unequivocal condemnation from the entire international community. ... It would make [Saturday] the bloodiest day since the unrest in Syria began in March 2011, with over 400 killed across the country."

Meanwhile, bloodshed continued in Syria's biggest city, Aleppo, where rebel-held areas came under heavy bombardment.

State television reported clashes between the army and "terrorists" in a central neighborhood of Aleppo next to the historic Old City and less than 1 km from its ancient citadel.

The Free Hauran Assembly activists' group said a brigadier named Mohammad Hassan al-Haj had defected to Jordan, the latest Sunni officer to desert.

But earlier reports that Vice President Farouq al-Sharaa had defected were shown to be wrong when he appeared in public for the first time in weeks, meeting Iranian officials, SANA reported.

Assad, who also met the Iranian parliamentary delegation in Damascus on Sunday, said Syria's crisis was the result of Western and regional states trying to crush the country's role in the "resistance" against Western and Israeli domination in the region.

"What is happening right now is not just a plot directed against Syria but the region as a whole, of which Syria is a foundational stone," he was cited as saying by state news agency SANA. "The Syrian people will not allow this plan to reach its goals, no matter the cost."

Alaeddin Boroujerdi, a senior member of Iran's parliament visiting Damascus, said, "Fortunately today important countries such as Russia, China and the Islamic Republic of Iran ... are completely opposed to imposed policies on Syria and foreign interference," Iran's Fars news agency reported. 

In a separate development, the head of the UN mission to Syria left the country after the mission had been wound up.

Senegalese Lt Gen Babacar Gaye joined a UN convoy to Lebanon on Saturday.

Last week, the UN decided against extending the mission, which was originally part of a six-point peace plan for Syria.

However, the ceasefire mandated by the plan never took hold and rising violence forced the UN monitors to be confined to their hotels since June.