The foreign ministers of Britain and France were to head to New York to make a fresh push for the UN Security Council to take action on Syria's bloody protest crackdown.
French Foreign Minister Alain Juppe and British Foreign Secretary William Hague were to press the council to adopt a resolution on Syria, where rights groups said 80 people were killed on Sunday alone.
US Secretary of State Hillary Clinton said that the council "must act" on Syria to end President Bashar al-Assad's "violent and brutal attacks" against demonstrators.
A French diplomatic source meanwhile said opinions had "evolved" within the council, with more members now willing to back a resolution.
"The balance within the Security Council has evolved" concerning a draft resolution on Syria, the source said.
"At least 10 countries" of the council's 15 members could vote in favour of a draft resolution, the source said, adding that the most hostile council members were Russia and India.
Veto-wielding Security Council member Russia meanwhile said it would not back a new draft resolution on Syria.
Russia had suggested to both Assad's regime and the opposition that they should meet in Moscow for "informal contacts" without any preconditions.
Russia and China placed a rare double veto on the first draft resolution last year, which placed the blame for the violence directly on Assad, a view dismissed by the West.
"The current Western draft has not gone too far from the October version, and, certainly, cannot be supported by us," said Russian Deputy Foreign Minister Gennady Gatilov.
The French diplomatic source said that the new non-permanent members of the Security Council were "more convinced of the need for a resolution."
Morocco, Togo, Guatemala, Pakistan and Azerbaijan joined the council as new temporary members this month. At the same time Brazil, which had been among countries resisting action in Syria, lost its place.
Juppe will seek "to persuade the Security Council to assume its responsibilities faced with the Syrian regime's worsening crimes against humanity," French foreign ministry spokesman Bernard Valero said.
"The situation in Syria is indeed dramatic and constantly worsening. Dozens of civilians have been killed in recent days by the Syrian regime's savage repression," Valero told journalists.
"It's time for the Security Council to be able to contribute to the resolution of this crisis. France supports the Arab League's efforts."
"The international community has repeatedly called on President Assad to stop the killing and repression of civilians," the British Foreign Office said in a statement announcing Hague was heading to UN headquarters.
"He has chosen to ignore these calls. As a result there is growing consensus that the world must speak up for the people of Syria."
It added: "Now is the time for the international community to unite, including by agreeing a United Nations Security Council Resolution this week, to make clear to President Assad and his regime that the killing must stop."
Arab League chief Nabil al-Arabi said on Sunday he hoped Russia and China would allow the UN Security Council to issue a resolution backing a new plan from the pan-Arab body to end the crisis.
The plan looks to secure a halt in the violence and Assad transferring power to his deputy ahead of negotiations, but the formula has been flatly rejected by Damascus.
A Russian diplomatic source told AFP that Foreign Minister Sergei Lavrov was currently on a tour of the Asia-Pacific region and "apparently he is not thinking of going to New York" for the Security Council meeting.