An international conference accepted a UN-brokered peace plan for Syria, but left open whether the country's president could be part of a transitional government.

The U.S. backed away from demands that President Bashar al-Assad be excluded, hoping the concession would encourage Russia to put greater pressure on its longtime ally to end the violent crackdown that the opposition says has claimed over 14,000 lives.

Moscow had refused to back a provision that would call for Assad to step aside, insisting that outsiders cannot order a political solution for Syria.

However, U.S. Secretary of State Hillary Clinton insisted that Assad would still have to go, saying "it is now incumbent on Russia and China to show Assad the writing on the wall."

'I will doubt that the Syrians who have fought so hard to have independence… will select people with blood on their hands to lead them.'—Syria envoy Kofi Annan

Foreign ministers from Europe, Turkey and three Arab countries representing groups within the Arab League were rushed from luxury sedans into the elegant and sprawling Palais des Nations along with their legions of diplomats, aides and envoys .

Syria envoy Kofi Annan said following talks that "it is for the people of Syria to come to a political agreement."

"I will doubt that the Syrians who have fought so hard to have independence … will select people with blood on their hands to lead them," he said.

The envoy earlier warned the permanent members of the UN Security Council — Britain, China, France, Russia and the United States — that if they fail to act at the talks hosted by the United Nations at its European headquarters in Geneva, they face an international crisis of "grave severity" that could spark violence across the region and provide a new front for terrorism.

"History is a sombre judge and it will judge us all harshly, if we prove incapable of taking the right path today," he said.

Warning for Moscow

He appeared to specifically aim his words at Russia, Syria's most important ally, protector and arms supplier.

"While many spoke of united support for one… some simultaneously took national or collective initiatives of their own, undermining the process. This has fueled uncertainty in Syria, in turn fueling the flames of violence," Annan said. "By being here today, you suggest the intention to show that leadership. But can you, can we follow through?"

He said that "the way things have been going thus far — we are not helping anyone. Let us break this trend and start being of some use."

Russia and China, which has followed Russia's lead on Syria, have twice used their council veto to shield Syria from UN sanctions.

'We haven't reached agreement in advance with Russia and China — that remains very difficult.'—British Foreign Secretary William Hague

Major regional players Iran and Saudi Arabia were not invited. The Russians objected to the Saudis, who support the Syrian opposition. The U.S. objected to Iran, which supports Assad's regime. Lavrov predicted the meeting had a "good chance" of finding a way forward, despite the grim conditions on the ground.

Syria, verging on a full-blown civil war, has endured a particularly bloody week, with up to 125 people reported killed nationwide on Thursday alone.

International tensions also heightened last week after Syria shot down a Turkish warplane, leading to Turkey setting up anti-aircraft guns on its border with its neighbour.

Without agreement among the major powers on how to form a transitional government for the country, Assad's regime — Iran's closest ally — would be emboldened to try to remain in power indefinitely, and that would also complicate the U.S. aim of halting Iran's nuclear goals.

UN monitoring mission could be scaled back

British Foreign Secretary William Hague urged Russia and China to join Western nations in speaking with one voice on Syria, though he acknowledged that will be a stiff challenge.

Hague noted that UN Secretary-General Ban Ki-moon told diplomats a UN monitoring mission in Syria would have to be pulled back if no diplomatic solution is found.

"We haven't reached agreement in advance with Russia and China — that remains very difficult. I don't know if it will be possible to do so. In the interest of saving thousands of lives of our international responsibilities, we will try to do so," Hague told reporters. "It's been always been our view, of course, that a stable future for Syria, a real political process, means Assad leaving power."

The head of the struggling UN observer mission, Norwegian Maj. Gen. Robert Mood, has described the 300 monitors approved by the UN Security Council to enforce a failed April cease-fire as being largely confined to bureaucratic tasks and calling Syrians by phone because of the dangers on the ground. Their mandate expires on July 20.

The negotiating text for the multinational conference calls for establishing a transitional government of national unity, with full executive powers, that could include members of Assad's government and the opposition and other groups. It would oversee the drafting of a new constitution and elections.

"Ultimately, we want to stop the bloodshed in Syria. If that comes through political dialogue, we are willing to do that," said Khalid Saleh, a spokesman for the Syrian National Council, a coalition of Syrian opposition groups based in Istanbul, Turkey. "We are not willing to negotiate (with) Mr. Assad and those who have murdered Syrians. We are not going to negotiate unless they leave Syria."

Clinton said Thursday in Riga, Latvia, that all participants in the Geneva meeting, including Russia, were on board with the transition plan. She told reporters that the invitations made clear that representatives "were coming on the basis of (Annan's) transition plan."

The United Nations says violence in the country has worsened since a cease-fire deal in April, and the bloodshed appears to be taking on dangerous sectarian overtones, with growing numbers of Syrians targeted on account of their religion. The increasing militarization of both sides in the conflict has Syria heading toward civil war.