Britain and France spearheaded a drive at the United Nations for a no-fly zone over Libya as battles raged across the country and Muammar Gaddafi's son said a civil war would erupt if his father stepped down.
The White House pushed back against rising pressure from some US lawmakers for direct intervention in Libya, saying it first wanted to figure out what military options could achieve in this oil-producing desert state which is racked by conflict.
Civilians were surrounded by Gaddafi forces in two western towns, Misrata and Zawiyah, and in the east warplanes hit the rebel-held oil terminal town of Ras Lanuf as strikes and counter-attacks pointed to an increasingly protracted conflict.
Two Arab papers and Al-Jazeera television said Gaddafi was looking for a pact allowing him to step down, but there was no official confirmation of the reports. Gaddafi in public has vowed to fight on and never leave Libya.
One of Gaddafi's sons, Saadi, said in an interview with Al-Arabiya television his father had not yet thrown his army into full battle against the rebels, saving it to shield Libya against foreign attack and to protect "sensitive sites".
"The tribes are all armed, there are forces from the Libyan army and the eastern region is armed. The situation is not like Tunisia or Egypt," said Saadi. "If something happened to the leader, who would be in control? A civil war would start."
The battlefield in eastern Libya around important oil terminals has become mired in attack and counter-attack between the loose-knit rebel army of young volunteers and defectors and the Libyan armed forces in a buffer zone of barren landscape between the east and the west of Libya.
The largely inexperienced rebels lack the firepower of their rivals. They have no warplanes to back them up and rely mostly on heavy machineguns, anti-aircraft weapons and rocket propelled grenades. They travel by 4x4 pick-up trucks.
But their agility, often fairly chaotic at the front, has given them a degree of protection from Gaddafi's forces, who have proved more effective at quashing the rebellion in the west around the Libyan leader's Tripoli powerbase.
UN aid coordinator Valerie Amos said the fighting across Libya meant that more than a million people fleeing or inside the country needed humanitarian aid.
"Humanitarian organisations need urgent access now," she said. "People are injured and dying and need help immediately." The United Nations appealed for $160 million for an operation over the next months to prepare shelter, food and medicine.
British Foreign Secretary William Hague said London was working with its partners "on elements of a resolution on a no-fly zone, making clear the need for regional support, a clear trigger for such a resolution and an appropriate legal basis".
A French source said France also was working with its UN partners on a no-fly zone resolution. Gulf states called for a no-fly zone and an urgent Arab League meeting.
Western allies differ over how a no-fly zone might be implemented. The United States has said it would involve a large-scale military operation, including strikes on Libyan air defences, but some military analysts have said it could be limited to preventing flights in Libyan airspace, without a big preliminary campaign.
US Defence Secretary Robert Gates, in Afghanistan where foreign forces have struggled for a decade, said action should be taken only with international backing. The White House said all options were on the table, including arming rebels.
Russia, a permanent member of the UN Security Council with veto powers, said it opposed foreign military intervention.
NATO Secretary-General Anders Fogh Rasmussen stressed the need for UN authorisation. "I can't imagine the international community and the United Nations would stand idly by if Gaddafi and his regime continue to attack their own people," he said.
NATO has launched 24-hour surveillance of Libya with AWACS reconnaissance aircraft, the US ambassador to NATO said.
US President Barack Obama said he wanted to "send a very clear message to the Libyan people that we will stand with them in the face of unwarranted violence and the continuing suppression of democratic ideals".
As the international community sought to isolate Gaddafi's government, Japan said on Tuesday it had imposed sanctions on Libya, including freezing assets of Gaddafi and several other Libyans, in line with a UN Security Council resolution.
"Based on the UN resolution, the cabinet agreed that Japan would carry out these measures, for the sake of unity with the international community," Japanese Finance Minister Yoshihiko Noda told a news conference after a cabinet meeting.
In the rebel-held city of Misrata, the wounded were being treated on hospital floors because of a catastrophic shortage of medical facilities in the besieged city, a resident said.
Misrata is the biggest city in the west not under the control of Gaddafi, and its stand against a militia commanded by his own son has turned it into a symbol of defiance.
Zawiyah, just 50 km (30 miles) from Tripoli, was in rebel hands despite a government forces' push, Sky television said.
In the east, warplanes launched strikes on the rebel-held oil town of Ras Lanuf 600 km (400 miles) east of the capital Tripoli. One ripped through a car carrying a family.
Shipping sources said the fighting had closed the Ras Lanuf terminal and the oil port of Brega. Brent crude prices rose above $118 a barrel on Monday before falling back to $115 and US prices pushed to their highest level since September 2008.
Youcef Yousfi, president of the Organisation of Petroleum Exporting Countries, said there were no plans for a crisis meeting of the group and high prices were short term.
The Libyan government says it is fighting against Al-Qaeda terrorists and maintains its security forces have targeted only armed individuals attacking state institutions and depots.
Al-Jazeera quoted sources from the rebel interim council as saying it rejected Gaddafi's proposal to quit because it would have been an "honourable" exit for him.
The channel said Gaddafi had wanted guarantees of safety for him and his family and a pledge they not be put on trial.
Jadallah Azous Al-Talhi, a former prime minister, earlier appeared on state television to urge rebels to "give a chance to national dialogue to resolve this crisis".
Ahmed Jabreel, an aide to rebel leader Mustafa Abdel Jalil, said: "Any negotiations must be on the basis that Gaddafi will step down. There can be no other compromise."
So far tens of thousands of migrant workers have fled but few Libyans.
"If we get a massive outflow of Libyans, this would create a refugee situation, so we appeal to all countries to keep their doors open and be ready to provide assistance as humanitarian law requires," UN High Commissioner for Refugees Antonio Guterres said.