Syrian opposition activists say scores of bodies have been found in a town near the capital, Damascus, accusing government troops of a “massacre”.
Many of those killed in the town of Darayya were victims of execution-style killings, the activists said.
According to unconfirmed reports, 200 bodies were discovered in houses and basement shelters.
Without commenting on the activists’ claim, Syrian state TV said Darayya was being “cleansed of terrorist remnants”.
The UK said that if the reports were confirmed, the killings would “be an atrocity on a new scale”.
Meanwhile, Syrian Vice-President Farouq al-Shara has greeted an Iranian delegation in Damascus, quashing weeks of speculation that he had defected to the opposition.
President Bashar al-Assad, who also met the Iranian delegation, said Syria would continue its current policy “whatever the cost” and accused Western nations of a regional conspiracy.