Washington says the Security Council may need to take measures that go beyond a no-fly zone in Libya.
France, Britain and the United States have pressed for a UN Security Council vote on Thursday on a no fly zone to halt Muammar Gaddafi's attacks on rebels.
Council ambassadors met behind closed doors to debate the text for more than eight hours on Wednesday, and said they would return on Thursday morning.
China's UN Ambassador Li Baodong, the current council president, told reporters "we hope we will have real progress tomorrow."
While China, Russia, Germany and other members of the 15-member council have expressed opposition or doubts about military action in Libya, the United States said that even stronger measures than a no-fly zone may be needed.
The council is discussing "a range of actions," including a no-fly zone, US ambassador Susan Rice told reporters after the deliberations.
Rice said the Obama administration is "fully focused on the urgency and the gravity of the situation on the ground, and it's my hope that we may be in a position to vote a serious resolution as early as tomorrow. We're working very hard toward that end.
"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."
Al Jazeera's Scott Heidler said that Rice's call for "a resolution that should go beyond a no-fly zone, is something that we haven't heard before.
"We are hearing from diplomatic sources that change came overnight on Tuesday when an initial draft resolution presented and discussed yesterday afternoon.
"She came into the discussions today [Wednesday] with a different point of view. And that was yes to no-fly zone and even a step further beyond a no-fly zone."
Final talks will be held before a vote and the draft could still be changed, diplomats from the three countries acknowledged.
Pressure on the council mounted as Libya's deputy UN envoy, Ibrahim Dabbashi, who has turned against Gaddafi, said "the international community has to act within the next 10 hours."
He said he had information that Gaddafi forces, backed by hundreds of mercenaries from Democratic Republic of Congo, Uganda, Burundi and Chad, were preparing major offensives in eastern and western Libya.
Gaddafi's forces have inflicted several defeats on rebels in recent days and US Secretary of State Hillary Clinton also hinted at a hardening Washington stance when she said the United States wanted a vote by the end of Thursday.
France and Britain had led the demands for a no-fly zone and French President Nicolas Sarkozy wrote to the heads of state or government of all the other council members seeking urgent backing for the measure.
"Together, we can save the martyred people of Libya. It is now a matter of days, if not hours," he said in the letter.
French Foreign Minister Alain Juppe said in Paris that several Arab countries had pledged to participate in possible military action in the North African country and Dabbashi confirmed that five Arab countries had already offered support.
Clinton said that the US administration was consulting with the Arab League "about their understanding of the goals and modalities of a no-fly zone as well as other forms of support."
"We believe that this must be an international effort and that there has to be decisions made in the Security Council in order for any of these steps to go forward," she said.
The no-fly zone is backed by the Arab League and the ambassador for Lebanon, the Arab representative in the Security Council, said several Arab states were ready to take part in the operation. He did not identify any states, however.
Gaddafi's son, Saif al-Islam, predicted in an interview with the Euronews channel that the rebellion would be over in 48 hours.
"I hope that the Security Council will prove Mr Saif Islam wrong," retorted the Lebanese envoy Nawaf Salam as he pressed for a tough resolution.
UN Secretary General Ban Ki-moon earlier on Wednesday urged all sides in Libya to accept an immediate cease-fire.
UN spokesman Martin Nesirky said Ban "is gravely concerned about the increasing military escalation by government forces, which include indications of an assault on the city of Benghazi."
The UN chief warned that "a campaign to bombard such an urban center would massively place civilian lives at risk," Nesirky said.
On the grounds, the Libyan army told people in Benghazi to leave opposition-held locations and arms storage areas.
A text on the screen of Al-Libya television addressed people in the eastern city, saying the army was coming "to support you and to cleanse your city from armed gangs".
"It urges you to keep out by midnight of areas where the armed men and weapon storage areas are located," it said.
Gaddafi said on Lebanon's LBC TV he did not expect a battle in Benghazi because Libyan people have been helping get rid of "al Qaeda" elements there.
Gaddafi, however, vowed that his forces would get engaged in a "decisive battle" on Thursday to recapture Misurata, the country's third city.
"The battle starts today (Wednesday) at Misurata and tomorrow, that will be the decisive battle," Gaddafi said in comments broadcast on Libyan state television.