GENEVA - -- Russia and China joined the United States Saturday in calling for a transitional government to replace the Bashar al Assad dictatorship in Syria, a major shift after a bloody conflict in which Assad has used the army and police to fight a pro-democracy uprising.

It suggested a significant move for Russia, which has backed Assad and his late father, Hafez, for 40 years. Earlier this month, Russian President Vladimir Putin joined President Barack Obama in a joint call for Syrians to democratically choose their own government, but stopped short of joining the call for Assad’s ouster. The question remained over how Moscow would implement the new policy.

At an all-day meeting of foreign ministers called by special envoy Kofi Annan, Russia, China, the U.S., Britain, France and several of Syria’s neighbors pledged to use their leverage on the Assad regime and on the opposition to stop the fighting and form an interim government with full executive powers.

Syria was not invited to the talks, nor, at U.S. insistence, was Iran, Syria’s single closest ally.

Annan said the agreement marked a new phase in the international response to the 16-month Syrian conflict that has left as many as 15,000 people dead.

“When the international community speaks with one voice, that voice becomes powerful and has an impact,” the former U.N. Secretary General told reporters. “We are seeing the international community coming together.”

At Russian insistence, the wording of the final communiqué did not explicitly call for Assad’s ouster but instead said the new government “shall be formed on the basis of mutual consent.”

It appeared to amount to the same thing. “The government will have to re-form by discussion, negotiation and by mutual consent, and I will doubt that the Syrians who have fought so hard for their independence, and to be able to have a say in how they are governed and who will govern, will select people with blood on their hands to lead them,” Annan said.

U.S. Secretary of State Hillary Clinton agreed. “Assad has to go. He will never pass the mutual consent test, given the blood on his hands,” she said at a separate news conference. She added that the agreement to vest the power to govern fully in the transitional governing body “strips him and his regime of all authority if he and they refuse to step down and leave.”

That message would have to be delivered by Russia and China.

She said the United States and its allies at the talks, including Kuwait, Iraq and Turkey, “made it absolutely clear to Russia and China that it is now incumbent upon them to show Assad the writing on the wall.”

If Syria’s allies in fact deliver that message and it leads in a transitional government, the Obama administration will have a strong counter to its Republican critics who have decried the U.S. failure to intervene on the side of the Syrian rebels.

But Annan and Clinton acknowledged there are some very tough hurdles ahead involving both sides in the Syrian conflict.

Annan, appointed joint special envoy by the United Nations and the Arab League, has been laboring since February to bring peace to Syria through a six point plan that has widely regarded as a failure. As of Saturday, he can call on an “action group,” consisting of the countries taking part in the Geneva talks, to back him up when his mediation effort hits an obstacle.