Dozens of people have been killed, activists say, in relentless shelling of rebellious suburbs of the Syrian capital of Damascus over the past two days. Most of the casualties were in the town of Douma.

The Local Coordination Committees and Britain-based Syrian Observatory for Human Rights and other activists say at least 40 people died in all-day shelling Thursday. At least two more were killed Friday morning.

The shelling is part of a fierce government offensive aimed at regaining control of parts of Damascus suburbs where rebels operate.

Douma in particular is a hotbed of dissent against President Bashar Assad's regime.

Government troops have been shelling Douma for days. Activists say most of those killed were civilians.

On Friday, International mediator Kofi Annan said he was "optimistic" that ministerial crisis talks on Syria being held on Saturday would produce an acceptable outcome.

"I think we are going to have a good meeting tomorrow. I am optimistic," Annan told Reuters TV in Geneva after Russia proposed changes to his plan for a national unity government. The talks would end "with an acceptable result," he said.

Meanwhile, U.S. Secretary of State Hillary Rodham Clinton and Russian Foreign Minister Sergey Lavrov were heading for a face-to-face showdown over Syria on Friday as the major powers prepared for the weekend meeting.