Libya: US urges tough United Nations resolution
US ambassador Susan Rice said a no-fly zone would only bring limited help. She hoped for an early vote on a draft.
Russia expressed concern at some of the implications of the proposals and put forward a counter-resolution.
Forces loyal to Col Gaddafi are taking ground from rebels, who say they fear "genocide" without swift UN action.
On Wednesday, the International Committee of the Red Cross withdrew from the rebel-held city of Benghazi, in eastern Libya, saying it feared an imminent attack by Col Gaddafi's forces.
Government forces say they have captured Ajdabiya, the last town before Benghazi, but the rebels deny this.
'Over in 48 hours'
The UN Security Council on Wednesday undertook lengthy and difficult negotiations over a resolution aimed at authorising a no-fly zone.
The US has previously been cool on the effectiveness of such a zone, but Ms Rice said further measures were now needed.
"The US view is that 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 BBC's Barbara Plett at the UN says the draft resolution contains controversial language authorising all necessary measures to protect civilians, which some interpret as permitting strikes against government ground forces if civilians are under attack.
She says that may have been what Russia's ambassador was referring to when he angrily declared that some members had introduced proposals with far-reaching implications.
Russia has strong reservations about military action, as does China, and instead offered a counter resolution calling first for a ceasefire.
Western diplomats said it was rejected because it lacked teeth.
Supporters of the draft resolution stressed the urgency of action and are pushing for a vote on Thursday; Kazinform cites BBC News.
See www.bbc.co.uk for full version