U.K. Prime Minister David Cameron said Syrian government and military officials responsible for violence against opposition protesters should be prosecuted for war crimes.

With little prospect of international military intervention to stop the bloodshed in Syria, as happened in Libya last year, and Russia and China blocking United Nations action, Cameron urged Syrian officials loyal to President Bashar al-Assad to switch sides.

“Make your choice: turn your back on this criminal regime or face justice for the blood that’s on your hands,” Cameron said at a news conference today in Brussels, where he attended a summit of European Union leaders. “However long it might take, the day of reckoning will come.”

The prime minister said that “the history of Homs,” the city where much of the opposition to President Bashar Al-Assad’s regime is focused, and which is currently under assault from government forces, “is being written in the blood of its citizens.” Homs is now a scene of “medieval barbarity,” he said.

Cameron urged China and Russia to “think again about supporting this criminal regime.”

To contact the reporter on this story: Robert Hutton in Brussels at rhutton1@bloomberg.net

To contact the editor responsible for this story: James Hertling at jhertling@bloomberg.net