A battle was raging on Friday between rebels and Muammar Gaddafi's forces for control of the airport in rebel-held Misrata, while fighting for a Libya border crossing into Tunisia hit a lull.

Loud blasts and gunfire early morning rocked Misrata's airport area, just southwest of the city limits, following overnight barrages of rocket and mortar fire launched by Gadaffi's forces on the besieged rebel bastion in western Libya.

Journalists reported further heavy detonations at around midday, and said the fighting was becoming more intense.

Western Misrata also came under seemingly indiscriminate mortar and rocket fire on Friday as a NATO warplane flew overhead, witnesses and medics said.

Gadaffi's forces were pushed back from Misrata, 215 kilometres, (132 miles) east of Tripoli, by the rebels and a series of NATO air strikes on Monday but remain within rocket range of the city.

The rebels said earlier in the week they had secured the port and their next objective was to take control of the airport, which is still in the hands of government troops.

"Attack is the best form of defence," said Ibrahim Bet-Almal, who heads the rebel military forces in the area.

"Gadaffi is sending reinforcements to the region every day," he added.

In western Libya, the situation at a post on the Tunisian border was calm on Friday morning following a day of heavy fighting, a reporter and witnesses said, adding that government troops appeared to have retreated into Tunisia.

They said the post at Dehiba was firmly in the hands of the rebels, who retook it on Thursday evening in clashes that killed eight loyalist soldiers, only hours after Gadaffi forces had overrun it.

The insurgents first captured the Dehiba post on April 21 and government troops have been battling to wrest back control ever since.

On the Libyan side of the border, the rival camps exchanged artillery fire in the early evening on Thursday, causing panic among civilians, a witness said.

Several ambulances from Tunisia crossed into Libya to evacuate the wounded, witnesses said.

A Tunisian police source said 5,150 people had crossed from Libya into Tunisia at Dehiba within 48 hours as the fighting raged.

Italy's military, meanwhile, took part in its first air raid over Libya, triggering an uproar within Prime Minister Silvio Berlusconi's coalition partner, the Northern League.

A pair of Tornado jets took off from Sicily equipped with precision-guided munition to strike 'selected targets', a defence ministry official said without revealing details.

In what was an about-face, Rome had said on Monday it would participate in air strikes with a NATO-led coalition against Gadaffi's regime.

While ruling out ground operations, the government said it was stepping up its contribution after heavy fighting in Misrata claimed numerous civilian victims.

The government decision is "a mistake that will end up in a wave of immigrants sent by Gadaffi or fleeing war," interior minister and senior Northern League member Roberto Maroni told the Libero daily.

The Thursday night shelling in Misrata was described as random, with two women and three children among those killed in the eastern district of Grara.

In other developments in Misrata, a prosecutor said government forces had kidnapped more than 500 people listed as missing.

"More than 500 people are listed at missing right now, and the number is going up each day," Tareq Alwash said. "I think a lot of people haven't been able to report others as missing because they can't contact us."

Alwash said 'many young people' were among those missing, 'generally aged between 10 and 20 ... and some women'. The youngest was named as nine-year-old Zacharia Ahmad.

In Brussels, rebel military chief Abdulfatah Yunis, formerly Gadaffi's interior minister, urged the West to deliver heavy weapons and warned that the strongman could use mustard gas on them in a bid to stay in power.

"Gadaffi is desperate now. Unfortunately he still has about 25 per cent of his chemical weapons, which maybe he will use since he's in a desperate situation," Yunis told a news conference.

In Paris, the military said French jets were dropping inert bombs packed with concrete instead of explosives to destroy Gadaffi tanks without killing civilians.

Spokesman Thierry Burkhard denied rumours that the use of the 300-kilogram (660-pound) training devices was prompted by a shortage of real bombs, adding that the first such strike crushed an armoured vehicle on Tuesday.