The US and the EU have again called on the Libyan leader Col Muammar Gaddafi to step down.
President Barack Obama said the US would take a wide range of actions to ensure Col Gaddafi surrendered power.
EU leaders meeting in Brussels agreed to "examine all necessary options" to protect the civilian population in Libya.But they made no mention of imposing a no-fly zone over Libya in their final communique.
British and French leaders had wanted leaders of the European Union's 27 member states to draw up plans to prepare to help the Libyan rebellion, including the possibility of a no-fly zone.
This would prevent pro-Gaddafi troops launching attacks from the air - currently the primary advantage the regime's troops have as they push back the rebel forces.
The rebels had captured many eastern towns in recent weeks in an uprising that followed protests inspired by the revolutions in Egypt and Tunisia.
But many other EU leaders were not keen on the idea of a no-fly zone.German Chancellor Angela Merkel said she was "fundamentally sceptical" about military intervention in Libya in general and about no-fly zones in particular.
The final communique did not mention a no-fly zone, although it also did not rule it out.
"In order to protect the civilian population, member states will examine all necessary options, provided that there is a demonstrable need, a clear legal basis and support from the region," the communique says.
France's President Nicolas Sarkozy said nobody wanted military intervention but "it is clear that Europe is sending a message and did not want to exclude this option".
But this would only happen, he said, with the support of the UN Security Council, the Arab League and the Libyan (rebel) authorities.
There were stronger words in Washington.
President Obama said the world had an obligation to prevent any massacre of civilians in Libya similar to those that took place in Rwanda and Bosnia during the 1990s.
He said that "we are slowly tightening the noose around Gaddafi" and "the bottom line is that I have not taken any options off the table at this point".
'Choke off revenue'
Mr Obama said an envoy would be appointed to consult with anti-Gaddafi representatives.
"Let me be as clear as I can about the desired outcome from our perspective, and that is that Gaddafi step down," he told reporters. "And we're going to continue to work with the international community to try to achieve that and we're going to be in close consultation with these opposition groups, as they get organised, to see how we can bring about that outcome."
EU leaders at the summit expressed political backing for the Libyan National Council, the interim authority set up by rebels in Benghazi, but stopped short of the diplomatic recognition given to the council on Thursday by France, a move which divided the bloc.
But leaders were more united over who they did not want in power, as summed up by European Commission President Jose Manuel Barroso.
"The problem has a name: Gaddafi. He must go," said Mr Barroso. "We have to intensify our international pressure on the current regime to step down."
The British Prime Minister David Cameron urged his EU partners to step up sanctions and choke off the revenue Col Gaddafi's regime gets from oil exports.
European Council President Herman Van Rompuy said leaders hoped to hold a joint summit soon with the Arab League and the African Union.
The Arab League is meeting to discuss the Libyan crisis on Saturday. The African Union has already rejected any idea of foreign military intervention in Libya.
Military momentum
The increased diplomatic push came as forces loyal to Col Gaddafi continued to make gains.
There have been more airstrikes on the oil port of Ras Lanuf, with an oil refinery and a rebel checkpoint among the targets. Rebels had earlier reported government forces entering the city by boat and in tanks.
The town has been held by anti-Gaddafi forces for several days and rebels still reportedly control the inner city and residential areas.
Col Gaddafi's regime took a number of Western journalists to Zawiya on Friday for the first time since it was recaptured from the rebels.
The city, 30 miles (48km) west of Tripoli, was shelled for days by government forces and reporters described scenes of devastation and streets that were deserted except for government supporters who had been brought in.
Reuters also reported strikes at Uqaylah and another bombing further east near Brega.
Thousands of people gathered in Benghazi after Friday prayers outside the courthouse, which has become the headquarters of the rebel council.
The CA's Pascal Harter in the city said vast crowds of people wearing the colours of the old Libyan flag were on the streets.
The head of the council, Mustafa Abdel Jalil, told the CA the rebels needed not only a no-fly zone but a sea embargo, weapons, and humanitarian assistance for the cities which have been besieged by Col Gaddafi's forces.
In a TV interview on Thursday, Col Gaddafi's son Saif al-Islam warned rebels in Benghazi that government troops were on their way.
In other developments:
- Gulf Arab states said the Gaddafi regime was illegitimate, and urged that contact be made with the rebels
- US President Barack Obama's top intelligence adviser James Clapper predicted government forces would defeat the rebels
- The CA News website appears to have been blocked by the Libyan authorities
- The International Committee of the Red Cross said that Libya had now descended into civil war
- New EU economic sanctions against Libya came into force on Friday, targeting the country's sovereign wealth fund and central bank