Rebels battling Moamar Gaddafi's regime say they have retaken the eastern town of Brega just hours after recapturing the strategic city of Ajdabiya in eastern Libya.

Earlier rebels moved into Ajdabiya, leaving a trail of destroyed tanks and military vehicles along the road after coalition air strikes ousted Mr Gaddafi's forces there.

It was their first significant victory since the launch of the Western-led strikes a week ago.

"We are in the centre of Brega," 80 kilometres west of Ajdabiya, rebel fighter Abdelsalam al-Maadani said by telephone.

"Gaddafi's forces are on the retreat and should now be at Al-Bisher [30 kilometres] west of Brega," he said, adding that the rebels "are also advancing towards this area."

A journalist travelling with the rebels saw rebel fighters in control of the centre of the oil town and said that government forces had completely withdrawn.

On March 13 the rebels abandoned Brega under heavy shelling from advancing government forces, and Libyan state television later that day declared the oil town "purged of the armed gangs."

The morale-boosting victory for opposition forces comes after eight days trying to break the town's siege.

The city lies on the front line between the two sides, and would have given the Libyan army a clear road to the opposition capital, Benghazi.

The signs of fierce fighting are all through the city, which bears the marks of shelling and missile fire.

The opposition says hundreds of people died in their homes, but there also signs of what a huge role the allied air forces have played in this battle, with the charred remains of Libyan army tanks scattered along the streets.

As news spread, thousands of people streamed into Ajdabiya, mostly to celebrate, but also bringing food and water.

'National interest'

News that rebels had control of Brega came as US president Barack Obama gave a staunch defence of his country's role in the international military mission in Libya.

Mr Obama has come under pressure to explain US goals to a public exhausted by wars in Iraq and Afghanistan.

His weekly radio and online address was his most detailed review of the UN-sanctioned action so far, and comes ahead of an address to the nation Monday on the US strategy in Libya.

"Make no mistake, because we acted quickly, a humanitarian catastrophe has been avoided and the lives of countless civilians - innocent men, women and children - have been saved," Mr Obama said.

Mr Obama said when innocent people were brutalised by a leader like Mr Gaddafi threatening a "bloodbath", and when nations were prepared to respond together, "it's in our national interest to act."

"And it's our responsibility. This is one of those times," he added. "Every American can be proud of the lives we've saved in Libya."

Conservative and liberal politicians have criticised Mr Obama for joining what many say is an open-ended, ill-conceived operation to enforce a no-fly zone over Libya.

But the president emphasised that the US mission "is clear and focused."

The UN Security Council mandated the no-fly zone and an international coalition that includes Arab countries was protecting Libyans to prevent "further atrocities."

"We're succeeding in our mission. We've taken out Libya's air defences. Gaddafi's forces are no longer advancing across Libya," he said.

He says it is an example of how the international community should work together and repeated that the US is not putting any ground forces into Libya.

- ABC/AFP