KABUL (Reuters) - British Prime Minister David Cameron said on Thursday that Syria's President Bashar al-Assad must step aside and there must be regime change in Damascus to avoid civil war.
"I would have a very clear message for President Assad, which is it is time for him to go, it is time for transition in this regime ... if there isn't transition it's quite clear there is going to be civil war," Cameron told reporters in Kabul during a trip to Afghanistan.
The U.N. Security Council put off a scheduled vote on a Syria resolution until Thursday and U.S. President Barack Obama telephoned President Vladimir Putin of Russia, Assad's main ally, to try to persuade Moscow to drop support for him.
"The message to (Russia's) President Putin ... and the message to all those on the U.N. Security Council, it is time for the U.N. Security Council to pass clear and tough messages about sanctions, I believe under Chapter 7 of the U.N., and to be unambiguous in this."
Al-Assad's brother-in-law Assef Shawkat, a top commander and one of the pillars of the Assad clan's rule, was killed in a bomb blast on Wednesday along with Defense Minister Daoud Rajha.
On Thursday morning, residents said there was no respite in the heaviest fighting to hit the city in a 16-month revolt against Assad's rule.
"The regime has done some truly dreadful things to its own people," Cameron said. "And I don't think that any regime that carries out acts as they have against their own citizens, and continue to do so by the way, should survive. I think that regime should go. So the message to President Assad is, it is time for transition, it is time for you to go."
Months of fierce clashes have killed 17,000 people, activists say. Western leaders fear the conflict, which has been joined by al Qaeda-style jihadists, could destabilize Syria's neighbors: Israel, Lebanon, Turkey, Iraq and Jordan.
(Reporting by Mohammed Abbas; Editing by Rob Taylor and Daniel Magnowski)