Libyan fighter jets have bombed anti-Gaddafi forces as the European Union (EU) called on the Libyan leader to go and Barack Obama urged the world to keep up the pressure.
"Colonel Gaddafi must relinquish power immediately," said an EU statement at the end of an emergency summit.
"His regime has lost all legitimacy and is no longer an interlocutor for the EU," it added.
The 27-nation bloc expressed "deep concern about attacks against civilians, including from the air". But it also stressed the need for "a clear legal basis and support from the region", reflecting divisions over the advisability of military intervention.
The legal basis sought by EU states would be a UN Security Council resolution authorising action.
The statement also called for an urgent summit between the EU, the African Union and the Arab League to discuss the crisis. French President Nicolas Sarkozy said that would take place "in the coming weeks".
The Arab League is due to meet in Cairo today. The African Union rejected military intervention in Libya, at a meeting in the Ethiopian capital Addis Ababa on Friday.
There was no mention in the final EU statement of calls from Britain and France for a no-fly zone over Libya - let alone Sarkozy's proposal for "targeted action" against Gaddafi.
In Washington, President Barack Obama told reporters: "Across the board, we are slowly tightening the noose on Gaddafi.
"He is more and more isolated internationally both through sanctions as well as an arms embargo," Obama said.
But he admitted he was worried about the threat Gaddafi still posed given the weapons at his disposal and reports that he had been hiring mercenaries.
"We're going to have to continue to apply pressure," Obama said, as the US Treasury Department hit another nine Gaddafi associates with sanctions, including his wife Safia Farkash and his defence minister.
The US has already frozen US$32 billion ($43bn) in Libyan assets. Obama also announced he would appoint envoys to meet the Libyan opposition.
Also in Washington, Libya's former ambassador to the UN, Abdel Rahman Shalgam, said Secretary of State Hillary Clinton would meet Mahmoud Jibril, the Libyan opposition National Council's foreign affairs chief, in Paris tomorrow.
However, in Libya, Gaddafi's fighter jets bombed rebel forces, as his forces tried to press their recent initiative.
Rebels said fighting had flared again in the key eastern oil hub of Ras Lanuf, after most were driven out in a battle on Thursday.
In the western city of Zawiyah, Gaddafi's troops fired into the air to celebrate the capture of the rebel stronghold. And the country's oil chief Shukri Ghanem said that operations had resumed after a three-day suspension at a key refinery in Zawiyah.
But in eastern, rebel-held Benghazi, up to 10,000 people poured on to the streets, calling for Gaddafi to go.
A UN mission would visit Libya today to evaluate its humanitarian needs, Gaddafi's deputy foreign minister Khaled Kaaim said in Tripoli.
In New York UN chief Ban Ki-moon said his envoy, former Jordanian foreign minister Abdul Ilah Khatib, would raise international concerns about Gaddafi's deadly crackdown on protests "in no uncertain terms".
The opposition, with its fighters in retreat, has appealed for foreign intervention.