On Thursday, British Foreign Secretary William Hague said his message to Assad is that "it is time to go."
He said the senseless killing must be brought to an end through a credible political process leading to a transition in Syria.
He also called on Assad to respond to a dialogue offer made recently by Syrian opposition chief Mouaz al-Khatib.
"A political settlement, a political agreement on a transition is the way forward in Syria to bring to an end this terrible and unacceptable loss of life."
Al-Khatib has said he is open to talks with the regime that could pave the way for Assad's departure, but that the Syrian leader must first release tens of thousands of detainees. The government has refused.
Hubbard reported from Beirut. Associated Press writer Zeina Karam contributed reporting from Beirut.