Britain's Foreign Secretary William Hague and French Foreign Minister Alain Juppe on Monday said they will attend UN talks scheduled for Tuesday.
Officials hope Qatari Prime Minister Hamad bin Jassim and Arab League officials can persuade Russia and China to back a UN Security Council resolution.
Russia says it won't support any resolution which could enable foreign military intervention.
British Prime Minister David Cameron's office says Russia's stance is "providing cover for the regime's brutal oppression."
The UN estimates about 5,400 people have been killed in 10 months of violence.