Syrian President Bashar Assad is losing legitimacy and should reform or quit, British Foreign Secretary William Hague said on Tuesday in the toughest language Britain has used during 12 weeks of protests in Syria.
"President Assad is losing legitimacy and should reform or step aside," Hague told parliament.
He said Britain was exploring with its European Union partners the potential for further sanctions against the Syrian government if the violence continued.
Earlier on Tuesday, Syrian and international human rights groups urged the world's top war crimes prosecutor to investigate the killing of more than 1,000 civilians during protests against Syrian President Bashar Assad.
The prosecutor's office at the International Criminal Court said it had received the request but its jurisdiction could only cover crimes committed in Syria by nationals of ICC member states.