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

But senior envoys who had gathered in Geneva were huddled in private meetings on Friday trying to come up with ways to break the deadlock on Syria's political transition after Russia proposed changes to Annan's plan, diplomats said.

"I think we are going to have a good meeting tomorrow. I am optimistic," the UN-Arab League envoy to Syria told Reuters Television in Geneva as he arrived for preparatory discussions.