The US has blamed Russia and China for the resignation of Kofi Annan as special UN envoy to Syria.

US Ambassador to the UN, Susan Rice, pointed the finger at the two members of the UN Security Council who blocked resolutions against Syrian president Bashar al-Assad - despite Annan imploring them to pass the sanctions.

"When the Security Council failed to heed Mr Annan's repeated calls for collective and significant consequences for non-compliance with its prior resolutions, those members who blocked this action effectively made Mr Annan's mission impossible," Rice said in a statement.

Rice also thanked Annan for his tireless efforts in trying to solve the Syria crisis.

Meanwhile, China has expressed regret over Annan's exit and says it will continue to work towards a political solution for the crisis.

"China expresses regret at Annan's resignation. We understand the difficulty of Annan's mediation work, and respect his decision. China supports the UN playing an important role in the appropriate resolution of the Syrian issue," said foreign ministry spokesperson Hong Lei.

"China believes that the international community should adhere to the correct direction of the political resolution in order to fundamentally settle the Syrian issue. China is open to any initiatives that are conducive to the political resolution of the Syrian issue," Lei added.

However Russian ambassador Vitaly Churkin said the fault for the previous deadlock lay with those countries which were most vocal in demanding Assad's resignation

"Those same countries who were pushing this resolution most actively are the countries who are providing weapons to the armed opposition groups, this is unfortunately the tragedy of the matter and something which made Kofi Annan's efforts so difficult," Churkin said.

New proposals

The UN General Assembly is gearing up to vote on a new set resolutions on 3 August, in an effort to bring Syria's 17-month civil war to an end.

The Saudi Arabia-drafted resolutions are likely to be passed with a simple majority by the 193-member assembly. However, reports suggest the draft has been toned down by diplomats, following the impasse which hampered earlier proposals.

Whereas the original draft, which was blocked by Russia and China, openly asked Assad to step down, it is believed the new text will not explicitly make such a demand.

"The aim is to increase pressure on the Assad government. We want as many people as possible to back this, which is why some changes have been made," an Arab diplomat told AFP.