An international conference to reach a political solution in Syria will include the opposition and take place at the same time as the UN considers a detailed plan to eradicate its chemical weapons.
French foreign minister Laurent Fabius said the chief opposition movement will be invited to the talks, which will take place in New York while the UN is meeting.
Top diplomats from the United States, France and Britain stood side by side to pressure Syrian president Bashar Assad to uphold his end of any deal on securing and destroying Syria's chemical weapons.
The United Nations Security Council is set in coming days to take up a resolution laying out plans for the agreement brokered by the United States and Russia.
"If Assad fails to comply ... we are all agreed, and that includes Russia, that there will be consequences," US Secretary of State John Kerry said.