Step down now, David Cameron urges President Assad
David Cameron has urged Syrian President Bashar al-Assad to step down to end the bloodshed in the country.
Thousands of people have died in fighting since a rebellion against the ruling regime began.
The UK prime minister told a committee of senior MPs that "the best path to peace" for Syria was a "transition at the top", not a bloody revolution.
He called the Assad regime, which has barred the Red Cross from the city of Homs, "illegitimate and criminal".
Mr Cameron was addressing the Liaison Committee, made up of chairmen of the Commons select committees which scrutinise government departments.
After a siege and bombardment of the Baba Amr district of Homs, lasting nearly a month, security forces moved into the area last Thursday following the withdrawal of armed rebels.
Last month China and Russia vetoed a United Nations Security Council resolution on Syria.
Russia said the document had singled out the government and did not contain measures against armed opposition groups, and China said "imposing a solution" would not help to resolve the issue.
Activists say 7,500 people have been killed since the uprising began almost a year ago. The Syrian government blames "terrorists and armed gangs" for the violence.
Mr Cameron, who spoke to Russia's Vladimir Putin following his victory in the country's presidential election at the weekend, said he had urged him to change his mind on the UN resolution but added: "I did not sense any sign of a shift."
He told the MPs: "I don't think we are ever going to agree on everything about Syria... but we need to agree that, at the very least, there's humanitarian access.
"I think they are absolutely wrong to take their position. They do have considerable influence in Syria. What they have done is very bad for their reputation across the Arab world.
"The Arab world is united in wanting to end the bloodshed in Syria."
The UN estimates 70,000 people have been displaced since the uprising began.
Mr Cameron said: "What's happening is absolutely appalling... The bloodshed being organised and carried out by this regime is criminal."
He added: "The best path to peace for Syria is a transition at the top of the regime, with Assad going... the idea of transition at the top is a better outcome, and less bloody, than a revolution at the bottom."
Asked whether the UK could help to arm the rebels, as happened in Libya last year, Mr Cameron replied: "At this point I think the right approach is to bring together the international community, put diplomatic pressure on the regime, work with the opposition to make sure they've got a proper outward face and then to work out what more we can do to help them pile the pressure on.
"I think we are at that stage, rather than going much further."