British Foreign Minister William Hague urged Russia and China to agree with Western powers on a political transition plan for Syria at a crisis meeting on Saturday but said the talks would be very difficult.

“There is an opportunity for the international community to be much stronger and act more robustly but we can only do it with the agreement of Russia and China,” he told reporters as he arrived for the talks at the United Nations in Geneva.

Foreign ministers from Western powers and Arab countries are attending a meeting convened by international mediator Kofi Annan in Geneva to try forge a common strategy to end the 16 month-old conflict in Syria but differences over the fate of Syria’s President Bashar Al Assad may thwart them.

“It has always been our view that a stable future for Syria, a stable political process means Assad leaving power as part of an agreement on transitional process,” Hague said.

US Secretary of State Hillary Clinton held talks on Friday night in St. Petersburg with Russian Foreign Minsiter Sergei Lavrov but failed to resolve differences.

Russia, Assad’s main ally, insists that any transition plan must not be imposed on Syria by foreign powers.

French Foreign Minister Laurent Fabius, arriving for the talks due to start at 0900 gmt, said: “It is absolutely essential that the violence stops and that a political transition can begin. Kofi Annan made reasonable propositions and I hope that they will be upheld and that’s the point of today’s discussions.”