The US has closed its embassy in Syria and Britain recalled its ambassador to Damascus in a new Western push to get President Bashar Assad to leave power and halt the murderous grind in Syria - now among the deadliest conflicts of the Arab Spring.
Although the diplomatic effort was blocked at the UN by vetoes from Russia and China, the moves by the US and Britain were a clear message that Western powers see no point in engaging with Mr Assad and now will seek to bolster Syria's opposition.
"This is a doomed regime as well as a murdering regime," Foreign Secretary William Hague told politicians as he recalled the UK's ambassador from Syria. "There is no way it can recover its credibility internationally."
President Barack Obama said the Syrian leader's departure is only a matter of time. "We have been relentless in sending a message that it is time for Assad to go," Mr Obama said during an interview with NBC. "This is not going to be a matter of if, it's going to be a matter of when."
The most serious violence was reported in Homs, where Syrian government forces, using tanks and machine guns, shelled a makeshift medical clinic and residential areas on the third day of a relentless assault, killing a reported 40 people, activists said. More than a dozen others were reported killed elsewhere.
Those deaths followed a regime onslaught in Homs that began on Saturday, the same day Syria's allies in Russia and China vetoed a Western and Arab-backed resolution aimed at trying to end the crackdown on dissent.
Some 200 people died, the highest death toll reported for a single day in the uprising, according to several activist groups.
Even as the US steps up pressure on Mr Assad to halt the violence and relinquish power, Mr Obama said a negotiated solution was possible, without recourse to outside military intervention.
Later, however, White House spokesman Jay Carney said the administration was taking "no options off the table".
In a signal that the window for diplomatic efforts may at some point close, Mr Carney said: "We need to act to allow a peaceful political transition to go forward before the regime's escalating violence puts a political solution out of reach."