Washington's ambassador to the United Nations, Susan Rice, urges the security council to pass a new resolution authorising aerial bombing of Muammar Gaddafi's tanks Reuters

The US is pushing the UN to authorise not just a no-fly zone over Libya, but also the use of air strikes to stop the advance of forces loyal to Muammar Gaddafi.

Washington's ambassador to the UN, Susan Rice, said on Wednesday that a no-fly zone would have only a limited use, and that the Obama administration was working "very hard" to pass a new resolution, which would authorise the use of aerial bombing of Libyan tanks and heavy artillery.

The UN security council is planning to vote on the resolution late on Thursday.

After a day of intensive negotiation in New York, Rice told reporters: "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."

The draft, supported by the US, Britain, France and Germany, reflects a significant 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.

Until this week, the US had been totally opposed to becoming involved militarily in Libya.

"We are interested in a broad range of actions that will effectively protect civilians and increase the pressure on the Gaddafi regime to halt the killing and to allow the Libyan people to express themselves in their aspirations for the future freely and peacefully," Rice said.

A diplomat on the security council told the Associated Press that Rice said the goal should be expanded from creating a no-fly zone to protecting civilians. To do this, the international community must have all the necessary tools – including authorisation to use planes, troops or ships to stop attacks by Gaddafi's air, land and sea forces.

The US, still fighting in both Iraq and Afghanistan, is deeply reluctant to be drawn into conflict in another Muslim country, and remains opposed to putting American troops on the ground to create "safe havens".

"The United States is pretty busy with two wars, and we don't want a third," a senior official told the New York Times.

Washington is insisting that any military action would have to be authorised by the security council and be carried out by an international coalition, including Arab states.

Barack Obama has been cautious over calls for a no-fly zone, which the Pentagon has described as a step tantamount to war.

But the secretary of state, Hillary Clinton, told reporters that the turning point was the Arab League's support over the weekend for a no-fly zone over Libya.

"That was an extraordinary statement," Clinton said, noting that Arab nations were asking the UN security council to take action "against one of their own".

Libya's deputy UN ambassador, Ibrahim Dabbashi, who supports the opposition, said five Arab countries have offered support, and told reporters he expects a no-fly resolution to be adopted, with a provision that will also allow air strikes.

Whether the security council does take action and authorises "all necessary measures" to protect civilians remains to be seen.

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

China's UN ambassador, Li Baodong, the current council president, told reporters "we hope we will have real progress tomorrow".