"A peaceful transition means that the regime needs to be changed. And that starts with the removal of the head of the state," Basma Kodmani, a spokeswoman for the Syrian National Council, an umbrella grouping various strands of the opposition, told Reuters Television.

"Mr. Annan's initiative for us should lead to developments of clear terms of reference for negotiation on the modalities of change. Not on whether the change should happen or not," she said on the sidelines of a meeting aimed at forging greater unity among opposition groups.

Assad's government said on Tuesday that it had accepted Annan's plan, but Kodmani said she would like to see action before believing its words.

"What we would like to see is the stopping of the killings," she said. "We would like to see protection of civilians if there is a possibility even of a two hours of truce to begin with, I think we welcome that and we will certainly work to make that succeed."