It was the highest death toll in the central neighborhoods of Damascus since the uprising erupted four months ago in the southern Hauran Plain near Syria's border with Jordan.

"Tens of thousands of Damascenes took to the streets in the main districts for the first time today, that is why the regime resorted to more killings," said one activist by telephone from Damascus. He declined to be named for fear of being arrested.

The killings prompted the opposition to cancel their planned National Salvation conference in the Qaboun neighborhood of Damascus on July 16 after security forces killed 14 protesters outside a wedding hall where the conference had been due to take place, said opposition leader Walid al-Bunni.

"Secret police also threatened the owner of the wedding hall. We decided to cancel the meeting to save lives," Bunni said via telephone from Damascus.

The rest of those killed in Damasacus were in Barzeh, where one protester died, and in the Rukn al-Din quarter of the city, where security forces fired on protesters killing eight people.

Two protesters were killed in the southern suburb of Qadam, according to the Local Coordination Committees.