Members of the UN Security Council expressed deep concern about the level of commitment to a ceasefire the Syrian government has demonstrated so far, US ambassador to the United Nations Susan Rice said on Tuesday. 

She added that the 15-nation body may soon face a "moment of truth" when it will have to decide whether or not to increase pressure on the government of President Assad, who has shown no signs of complying with a Tuesday deadline to withdraw forces from towns and stop using heavy weapons.

Her remarks appeared to be aimed at Russia and China, which have twice vetoed resolutions condemning the violence but have recently supported several council statements backing UN-Arab League envoy Kofi Annan's peace plan. [Reuters]