British Foreign Secretary William Hague said Saturday he was uncertain that world powers could reach a power transition deal to halt the bloodshed in Syria, as Russia and China remain opposed.

"We haven't reached agreement in advance with Russia and China. That remains very difficult and whether it will be possible, I don't know if this will be possible," he told reporters on arriving at the United Nations in Geneva for talks on the crisis hosted by international envoy Kofi Annan.

Hague stressed that "a stable future for Syria means (President Bashar al-Assad) leaving power."

However, Moscow and Beijing take a different view, with Russia earlier angrily dismissing Annan's proposal that implies that Assad would have to relinquish his grip on power for a transition plan to succeed.

The disagreements had threatened to scupper Saturday's meeting between foreign ministers of the five permanent Security Council states the US, Russia, Britain, China and France, as well as regional powers Qatar, Turkey, Kuwait and Iraq.

At the 11th hour, Russia issued an upbeat statement ahead of the meeting, but insisted that Assad's fate "must be decided within the framework of a Syrian dialogue by the Syrian people themselves."

Hague said that despite the difficulties, world powers would try to reach a deal Saturday: "In the interests of saving thousands of lives and of our international responsibilities, we will try to do so."

"There will be no point signing up to a worthless agreement or one that does not advance the situation so we go into it with that spirit today."

He also called on parties to agree on applying sanctions under Chapter 7 of the Security Council resolution if Syria failed to apply Annan's peace plan.

"In our view there should be a Chapter 7 resolution of the Security Council mandating and requiring the implementation of that plan with consequences if it is not implemented.

"But we can only do that with the cooperation of the Russians and the Chinese," he added.

Russia and China have been opposed to sanctions.

Annan's peace plan had required a ceasefire in Syria on April 12, but violence has raged on since, with rights monitors saying that more than 230 people -- most of them civilians -- had been killed across the strategic Middle East country since Thursday alone.