Nato said it would enforce a Libya no-fly zone but stopped short of taking full command of UN-backed military operations.
Western warplanes hit Libya for a fifth night on Thursday, but have so far failed to stop Muammar Gaddafi’s tanks shelling rebel-held towns.
Western warplanes silenced Muammar Gaddafi’s artillery and tanks besieging the rebel-held town of Misrata on Wednesday.
Western powers pounding Libya’s defences will wind up in the dustbin of history, said leader Muammar Gaddafi as his troops held back rebel advances.
Anti-aircraft fire rang out across Tripoli for a third night on Monday, but air attacks on Libya are likely to slow.
Western powers launched a second wave of air strikes on Libya early on Monday.
Western forces hit targets along the Libyan coast on Saturday, using strikes from air and sea to force Muammar Gaddafi’s troops to cease fire.
The United States accused Muammar Gaddafi of defying international demands for an immediate ceasefire.
Europe and the US stepped up pressure on Muammar Gaddafi to quit, while on the ground his forces used their strength to press their advantage.
Nato and the EU begin two days of talks on Libya on Thursday focusing on a possible "no-fly" zone after a day of fierce fighting.