Elite troops backed by tanks massed round the Syrian protest city of Homs on Wednesday as Washington worked on a UN Security Council draft resolution demanding humanitarian access to trapped civilians.

China said it backed sending international aid as diplomats said the new text being drawn up by Washington focused on getting relief into cities under assault in a bid to avoid a third set of vetoes from Beijing and Moscow.

Washington said it opposed sending weapons to opponents of President Bashar al-Assad for fear that Al-Qaeda was exploiting the more than 11-month uprising against his regime after key US ally Saudi Arabia voiced strong support for arming the rebels.

Activists on the ground in Syria’s third-largest city said that elite troops of the Fourth Armoured Division under the command of Assad’s brother Maher had taken up position with their armour around the rebel stronghold of Baba Amr.

Hadi Abdullah of the Syrian Revolution General Commission told AFP by telephone that it was a likely prelude to a final assault.