Rebels downed a military aircraft on Monday as they fought a government bid to take back Libya's third city, Misrata, a witness said, while foreign ministers discussed how to help them oust Muammar Gaddafi.
Gaddafi's forces have been trying for days to push back a revolt that has won over large parts of the military, ended his control over eastern Libya and is holding the government at bay in western cities near the capital Tripoli.
In both Libya's third city, Misrata, 200km to the east, and Zawiyah, a strategic refinery town 50km to the west, rebels with military backing were holding the town centres against repeated government attacks.
"An aircraft was shot down this morning while it was firing on the local radio station. Protesters captured its crew," the witness, Mohamed, told Reuters by telephone.
"Fighting to control the military air base started last night and is still going on. Gaddafi's forces control only a small part of the base. Protesters control a large part of this base where there is ammunition."
Foreign governments are increasing the pressure on Gaddafi to leave in the hope of ending fighting that has claimed at least 1,000 lives and restoring order to a country that accounts for two percent of the world's oil production.
The UN Security Council has slapped sanctions on Gaddafi and other Libyan authorities, imposed an arms embargo and frozen Libyan assets, while making clear that those who used violence against civilians would face international justice.
US Secretary of State Hillary Clinton, Russian Foreign Minister Sergei Lavrov, European Union foreign policy chief Catherine Ashton and others were holding bilateral talks at a human rights conference in Geneva to coordinate further action.
European powers including erstwhile ally Italy said it was time for Gaddafi to quit and Clinton said the United States was "reaching out" to opposition groups.
A US official in Geneva said a central aim of sanctions was to "send a message not only to Gaddafi ... but to the people around Gaddafi, who are the ones we're really seeking to influence".