Kofi Annan, the joint UN-Arab League envoy to Syria has said he was "optimistic" that the ministerial crisis talks on Syria would produce an acceptable outcome.

"I think we are going to have a good meeting tomorrow [Saturday]. I am optimistic," Annan told Reuters Television in Geneva on Friday.

The talks being held by foreign ministers of major powers and regional players in the Swiss city will end "with an acceptable result", he said, without giving details.

Rare insights into life in Homs under daily shelling

Russia proposed changes on Thursday to his plan for a national unity government in Syria, despite initially supporting it, but the United States, Britain and France rejected the amendments, Western diplomats said.

The suggested changes are related to Moscow's refusal to support the ouster of Syrian President al-Assad, diplomats in New York said on condition of anonymity.

Foreign ministers from Turkey, Kuwait, Qatar and Iraq will also attend the meeting. Iran, Assad's other close ally, was excluded - a condition set down by the US - as was Saudi Arabia, which has supported the Syrian opposition.

Annan's spokesman Ahmad Fawzi told Reuters: "The talks are on course and the preparatory meeting is going ahead this morning [Friday]."

'Massacre' in Damascus suburb

Assad on Thursday dismissed the notion of any outside solution to the 16-month-old uprising against his rule.

"We will not accept any non-Syrian, non-national model, whether it comes from big countries or friendly countries. No one knows how to solve Syria's problems as well as we do," Assad said on Iranian state television.

Spotlight In-depth coverage of escalating violence across Syria

The latest development came as activist reported a "massacre" in the Damascus suburb of Douma, about 15 km (9 miles) outside the capital Damascus.

At least 51 people have reportedly killed and scores of others injured there, amid reports of heavy bombardment in the city for a 24th day.

Of those killed on Thursday, activists said that 10 were executed by pro-regime militias at a checkpoint as they tried to flee the shelling.

A Video published on YouTube showed rows of shrouded bodies lining what activists said was a street in Douma.

Also on Thursday, two bombs exploded outside the Palace of Justice in central Damascus, state television reported, without giving any immediate word on any casualties.