Opposition activists Monday accused Syrian government forces of committing a new massacre, with pictures posted online showing dozens of piled bodies covered in blood in the outskirts of Damascus.

They said some people had been killed by troops in the suburb of Hazza.

The report comes after the Local Coordination Committees, a group of activists documenting violence in Syria, said that the death toll in August had reached 5,000 - the bloodiest month since the uprising against President Bashar Assad began in 2011.

On the diplomatic front, Damascus announced it would cooperate with the new international peace envoy, Lakhdar Brahimi, as it had done with his predecessor, Kofi Annan.

"We will listen to him and he will listen to us," Jihad Makdissi, Syrian Foreign Ministry spokesman, said in an interview with a pro-Syrian Lebanese television.

"We tried with Mr. Kofi Annan... the reasons that led to his initiative's failure were not Syrian. The main reason was a lack of international consensus," he said.

Brahimi is to visit Cairo and Damascus this month for talks with the Arab League and government officials.

Diplomatic attempts to end the Syrian conflict are "nearly impossible" and not enough is being done to end the fighting, the new U.N. and Arab League mediator Lakhdar Brahimi said in a BBC interview broadcast on Monday.

"I know how difficult it is - how nearly impossible. I can't say impossible - nearly impossible," Brahimi, an Algerian diplomat told the BBC. "And we are not doing much. That in itself is a terrible weight."