The United Nations security council is planning to vote later on Thursday on a draft resolution that would not only introduce a no-fly zone over Libya

The United Nations security council is planning to vote later on Thursday on a draft resolution that would not only introduce a no-fly zone over Libya but would authorise the use of air strikes to stop the advance of forces loyal to Muammar Gaddafi.

The draft, supported by the US, Britain, France and Germany, reflects a shift by Washington, alarmed by the speed at which the uprising is collapsing and concerned at the possibility of a massacre in the rebel stronghold of Benghazi.

The US until this week had been totally opposed to becoming involved militarily in Libya.

The US ambassador to the UN, Susan Rice, told reporters on Wednesday night after a day of intensive negotiation: "We need to be prepared to contemplate steps that include, but perhaps go beyond, a no-fly zone at this point, as the situation on the ground has evolved, and as a no-fly zone has inherent limitations in terms of protection of civilians at immediate risk."

Although a vote has been pencilled in for Thursday afternoon, schedules have a tendency to slip at the UN. Russia and China, which both have a veto on the the 15-member security council, could yet block it.

A UN resolution would pave the way for military action that could involve the US, and other members of Nato such as Britain and France, as well as Arab states. The US remains opposed to putting troops on the ground to create 'safe havens' and instead sees planes being used to stop tanks advancing towards Benghazi or ships loyal to Gaddafi bombarding the city.