Ms. Clinton said Americans and Europeans must send a clear and common message to despots that they must respect the rights of their people. "As a tyrant in Damascus brutalizes his own people, America and Europe stand shoulder to shoulder," she said.

"We are united, alongside the Arab League, in demanding an end to the bloodshed and a democratic future for Syria. And we are hopeful that at 10 a.m. Eastern Standard Time in New York, the Security Council will express the will of the international community."

Her comments came as Barack Obama condemned Assad for the "unspeakable assault" on Homs in which 200 people were killed and called for the Syrian leader to step down.

Clinton added: "Wherever tyrants deny the legitimate demands of their own people, we need to work together to send them a clear message: you cannot hold back the future at the point of a gun."