The Guardian reports: Bashar al-Assad has been warned to implement a UN-backed peace plan to end more than a year of violence in Syria, amid growing scepticism at the lack of international resolve to tackle the bloodiest crisis of the Arab spring.

Hillary Clinton, the US secretary of state, issued the threat at a conference of the Friends of the Syrian people in Istanbul on Sunday, but there was little evidence of coherent international action if he does not comply.

Syria announced last week that it had accepted a six-point plan being promoted by the former UN secretary general Kofi Annan, though Assad then demanded that the “armed terrorist groups” he says are supported by an Arab-western “conspiracy” disarm first. According to the UN, 9,000 people have been killed in Syria over the last year.

“Nearly a week has gone by, and we have to conclude that the regime is adding to its long list of broken promises,” Clinton told the representatives of 83 countries as pro-Assad protesters demonstrated outside the conference venue. “The world must judge Assad by what he does, not by what he says. And we cannot sit back and wait any longer.”

Russia and China, traditional allies of Assad, stayed away from the meeting, while Syrian officials and media scorned it. Opposition activists, under pressure to close ranks, appeared less divided than before, but many dismissed the event as a display of impotence or even as an April Fool’s Day Joke.

Annan’s six-point plan calls for a ceasefire, military withdrawals from towns, prisoner releases, humanitarian and media access and above all a “Syrian-led” political process to negotiate transition to a new government.

On Saturday, the Damascus regime claimed victory over its enemies, declaring an end to the 13-month uprising and the start of a new stage of “stabilisation”.

But the repeated calls in Istanbul to adopt the Annan plan sounded half-hearted. Annan, who is due to brief the UN security council on Monday, did not even attend.