But they still disagree on whether President Bashar al-Assad needs to go.
As the meeting got under way, the opposition in Syria posted a video online showing what they said was a government mortar attack on a funeral procession which killed more than 30.
The United Nations peace envoy, Kofi Annan, gave details of the peace plan after the talks between delegates from the Arab League, Russia and the United States.
He warns that without the establishment of a government of national unity, Syria faces a catastrophe.
"The transitional governing body could include members of the present government and the opposition and other groups should be formed on the basis of a mutual consent," he said.
Pressed if members from the regime who have engaged in repression would be part of the interim government, he said: "People with blood on their hands are hopefully not the only Syrians.
"I would doubt that Syrians... would select people with blood on their hands to lead them."
Asked what the transition plan spelled for President Assad, the envoy said: "The document makes it clear that we have provided guidelines and principles to assist the Syrian parties as they move ahead with the transition and establish a transition government and go through changes required."
The future of Assad "will be left to them".