AJDABIYA, Libya – Libyan leader Moamer Kadhafi suffered a major blow Wednesday with the defection of his foreign minister even as his forces again proved too strong for the rebels' rag-tag army.

Foreign minister Mussa Kussa became the most senior figure yet to defect from the Kadhafi regime since a popular uprising against his iron-clad 42-year rule erupted more than six weeks ago in the eastern city of Benghazi.

"We can confirm that Mussa Kussa arrived at Farnborough Airport on 30 March from Tunisia," the British foreign ministry said. "He travelled here under his own free will. He has told us that he is resigning his post."

"Mussa Kussa is one of the most senior figures in Kadhafi?s government and his role was to represent the regime internationally, something that he is no longer willing to do," the British statement added.

Libyan rebels were driven back some 200 kilometres (125 miles) on Wednesday by the superior firepower of Kadhafi's forces in a chaotic stampede which saw them yield most of the ground their recent advances had secured.

The first air strike from the NATO-commanded allied coalition in two days against loyalist positions in the east brought them some cause for celebration.

But Kadhafi's forces overran the towns of Ras Lanuf, Uqayla and Brega, rebels reported, scattering the outgunned insurgents as world powers mulled arming the fighters to help them oust the Libyan strongman.

AFP reporters and rebel fighters said Kadhafi's troops swept through the oil town of Ras Lanuf, 300 kilometres (185 miles) east of Kadhafi's hometown Sirte, soon after dawn, blazing away with tanks and heavy artillery fire.

But later, an air strike about 10 kilometres (6.5 miles) west of Ajdabiya, where rebels are sheltering, sent a huge plume of smoke rising into the sky and brought cries of jubilation from the rebel fighters, who had been calling for renewed air support.

"We want two things: that the planes drop bombs on Kadhafi's tanks and heavy artillery; and that they (the West) give us weapons so we can fight," rebel fighter Yunes Abdelghaim told AFP.

The 27-year-old, who was holding a Russian AK-47 assault rifle and French flag, said it seemed as if the coalition had halted its air strikes for two days coinciding with a London conference on the Libyan crisis.

"We want the French to bomb the (Kadhafi) soldiers," said another fighter, Ali Atia al-Faturi, as the sound of shelling and gunfire grew louder.

By nightfall, the town of Brega, which also has an oil refinery, was in the hands of loyalists, rebels said, and the sound of artillery fire could be heard on the outskirts of Ajdabiya.

A spokesman for the rebels played down allegations by a top NATO commander that there may be Al-Qaeda fighters in their ranks, but said his fighters had come up against a force of thousands of Chadian Republican Guards.

Colonel Ahmed Bani told reporters in the rebel stronghold Benghazi: "If there are any Libyans who were associated with Al-Qaeda around the world and are now in Libya, they are fighting on behalf of Libya. If," he emphasised.

Of the hasty retreat, he said: "We found that the best response was a tactical retreat until we can develop a better strategy for confronting this force." There were between 3,200 and 3,600 heavily armed troops, he said and claimed to have "three sources" for the presence of the foreign soldiers.

NATO began to take command of Libyan air operations from a US-led coalition as warplanes and other assets from several allies came under the military organisation's control.

"Today NATO aircraft are flying under NATO command in the Libyan sky," NATO spokeswoman Oana Lungescu told AFP.

"This is a phased process, which will be completed as soon as all allies and partners have transferred authority for their assets," Lungescu said.

As the insurgents were being routed, British Prime Minister David Cameron said in London that the option of arming the rebellion had not been ruled out, putting him more in line with US President Barack Obama.

Asked in parliament what Britain's policy was on arming the rebels, given the existence of a United Nations arms embargo on Libya, Cameron replied: "We do not rule it out but we have not taken the decision to do so."

French Foreign Minister Alain Juppe had set the tone at the London conference when he said on Tuesday that France was prepared to hold discussions on delivering arms to the rebels.

Russian Foreign Minister Sergei Lavrov said however Moscow believed that foreign powers did not have the right to do so under the mandate approved by the UN Security Council.

And in Beijing, China's President Hu Jintao warned French President Nicolas Sarkozy that air strikes on Libya could violate the "original intention" of the UN resolution authorising them if civilians suffer.

US Secretary of State Hillary Clinton said that although UN sanctions prohibit the delivery of arms to Libya, the ban no longer applies.

"It is our interpretation that (UN Security Council resolution) 1973 amended or overrode the absolute prohibition on arms to anyone in Libya, so that there could be a legitimate transfer of arms if a country should choose to do that," she said.

A spokesman for the rebel Transitional National Council, Mustafa Ghuriani, told reporters "it would be naive to think we are not arming ourselves" to match the weaponry deployed by Kadhafi loyalists.

But he declined to confirm or deny that France and the United States were offering to supply arms, saying only that unspecified "friendly nations" were backing the rebels.