In a fresh challenge to the interim government's weak authority, members of the al-Awfea Brigade occupied the airport for several hours demanding the release of their leader whom they said was being held by Tripoli's security forces.

An Italian passenger who was due to fly out and later arrived at a Tripoli hotel described the situation as chaotic.

"There were about 200 of them who came into the airport, they were armed. We were waiting to board our flight and we could hear noises, people shouting," he said.

Leaders of militias which became part of the government's official security forces after the war which ousted Muammar Gaddafi said they had intervened to stop the fighting, in which they said 10 people were injured, without government leadership.

Government spokespeople were not available for comment much of the day but later said the situation had been resolved.

"The airport will resume operation within 24 hours. I heard there were some injured," government spokesman Nasser al-Manee told a late night press conference, without giving a number of those wounded in the clashes.

Weeks before a planned election, Libya's new rulers are struggling to assert control over an array of former fighters who still refuse to lay down their arms after last year's war.

STAND OFF AND NEGOTIATIONS

In a dramatic move, 60-to-70 armed militia vehicles from the al-Awfea Brigade ambushed the airport's tarmac from adjacent open fields. Surrounding the planes, the militiamen forced some passengers off the planes, a brigade fighter said.

A member of the Awfea militia, which came from the city of Tarhouna, 80 km southeast of Tripoli, said the militia believed their leader, Colonel Abu Oegeila al-Hebshi, had been detained by the Tripoli Security Committee on Sunday night.

"We are protesting his kidnapping by coming to this airport," Anas Amara said. "We have one tank outside the airport and our cars are surrounding the airplanes so they don't fly."

Violence later broke out when militia groups from Tripoli and the mountain town of Zintan arrived to try to get the Awfea militia to leave the airport.

Hakim Buhagir, leader of a Tripoli brigade, said they persuaded the Awfea fighters to hand over their weapons.

"We negotiated with them and promised them we would help find their leader within three days and they were convinced," he said. "We let them go after confiscating their heavy weapons and drafting a list of their names."

NO GOVERNMENT INTERVENTION

By nightfall former fighter brigades had helped to restore calm, but the airport remained non-operational.

Eleven planes including Austrian Airlines and Alitalia aircraft stood vacant on the tarmac, and more than 30 pickup trucks fitted with anti-aircraft weapons stood idle nearby, securing the location.

Fighters smoked and chatted near their cars, swinging their Kalashnikovs over their shoulders and sometimes firing anti-aircraft rounds into the air in celebration.

"The revolutionaries of Libya freed the airport today, not the government," Essam al-Gatous, leader of one brigade, said.

Monday's violence is the latest in a series of incidents as the North African country prepares for its first free polls for a national assembly since last year's war.

Disgruntled former fighters have held regular protests that at times have turned violent. Last month, one person was killed and several were wounded when militiamen protesting outside the prime minister's office started shooting.

In November, about 100 Libyans surrounded a Tunisian passenger aircraft at Tripoli's Mitiga airport, delaying its takeoff in an anti-government protest.

(Additional reporting by Marie-Louise Gumuchian and Ali Shuaib; Writing by Hadeel Al-Shalchi and Marie-Louise Gumuchian; Editing by Michael Roddy)

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