Libyan insurgents and civilians stampeded out of Ajdabiya on Thursday on rumours that loyalist forces were outside the eastern town, hours after a rebel armoured unit was hit by apparent NATO friendly fire.

A rebel lorry with a rocket launcher is seen through the Libyan rebellion\'s flag in Ajdabiya.

The panic came as a top US general said it was unlikely the rebel forces could launch an assault on Tripoli and oust Moamer Kadhafi, though France confidently predicted the strongman\'s downfall.

And as loyalist forces continued to besiege the rebel held city of Misrata and challenge the rebels on other fronts, Turkey\'s prime minister called for Kadhafi to stop his onslaught and to pull back.

Families packed into cars and trucks joined rebel military vehicles in a charge northeast towards the insurgent stronghold of Benghazi, some 160 kilometres (100 miles) away, AFP correspondents said.

The administrator of the hospital in Ajdabiya said many civilians fled in panic because of the unconfirmed rumours of advancing Kadhafi forces, but that the rumours were unfounded.

Many rebel fighters remained in the town along with doctors at the hospital, after its patients were evacuated to Benghazi as a precaution, Majbali Yunis said by telephone.

The flight began soon after rebel tanks were hit by an air strike near the key oil town of Brega, 80 kilometres west of Ajdabiya.

General Abdelfatah Yunis, the rebel commander, said in Benghazi that four people -- two fighters and two medics -- were killed in the Brega attack, 14 wounded and another six people were missing.

He said "we think it was friendly fire, carried out in error by NATO," adding that the rebels had informed NATO that they were moving T55 and T72 heavy tanks from Benghazi to Brega.

"We suffered a setback today," he added, but said the rebels have 400 tanks and will get more.

Separately, a doctor said a nurse was killed and two wounded when an ambulance in the Brega sector was hit by shrapnel from an unknown source.

The fighters, already angry at what they perceive to be lack of air support from NATO, which is enforcing a UN no-fly zone over Libya to protect civilians, vented their fury over the strike.

"Instead of attacking Kadhafi they are attacking us," said Suleiman Rifadia, a volunteer medic at the hospital.

"How come NATO is dropping bombs east of Brega when Kadhafi\'s forces are to the west?" asked another rebel fighter, Omar Mohammed.

Saleh Faraj, a former soldier siding with the rebels, said at least three rebel tanks were hit in the air strike.

"There was no fighting anywhere. (The warplanes) flew back and forth and then they struck our forces," said Faraj.

In Brussels, NATO said it was trying to confirm the reports, but it warned that it would strike any forces threatening civilians.

Rebels seized Ajdabiya on March 26, a week after coalition forces, through air strikes and cruise missiles, beat Kadhafi\'s forces back from the gates of Benghazi.

After edging to within 60 kilometres of Kadhafi\'s hometown of Sirte on March 28, the rebels have since been steadily pushed back almost 400 kilometres by the superior fire power of Kadhafi\'s forces, despite the coalition air strikes.

It was unclear on Thursday exactly where the front line was or whether any rebels were making a stand against Kadhafi\'s army.

Despite Kadhafi\'s apparent battlefield advances, France said it was now only a question of how his regime meets its downfall rather than whether the veteran Libyan ruler can survive in power.

"The question today is to know under what conditions Kadhafi goes, not how he\'s going to be able to hold on to power," Foreign Minister Alain Juppe told lawmakers in Paris.

However, General Carter Ham, head of US Africa Command, said in Washington it was unlikely the rebel forces could push Kadhafi out.

Asked at a Senate hearing about the chances that the opposition could "fight their way" to Tripoli and replace Kadhafi, Ham replied: "Sir, I would assess that as a low likelihood."

His comments underscored growing concern in Washington and European capitals that the conflict is heading toward a stalemate, with Kadhafi firmly in control in Tripoli and badly organised rebels unable to turn the tide even under the cover of NATO-led air power.

Besides being routed in the east, the rebels are struggling to defend Misrata, Libya\'s third city, under an onslaught from better armed regime forces.

The United Nations called for a halt to hostilities around Misrata, about 215 kilometres (130 miles) east of Tripoli, saying several weeks of "heavy shelling" by Kadhafi\'s forces had killed or wounded hundreds.

UN chief Ban Ki-moon made a new "urgent call for an immediate cessation of the indiscriminate use of military force against the civilian population," his spokesman said.

"Conditions in Misrata are especially grave, with reports of the use of heavy weapons to attack the city, where the population is trapped and unable, as a result of heavy shelling that has continued over several weeks, to receive basic supplies, including clean water, food, and medicines," he said.

NATO said government troops are using civilians as human shields in Misrata, making its task more precarious.

Turkey\'s Recep Tayyip Erdogan said "a real ceasefire (in Libya) should be settled immediately and military units of Kadhafi should remove the siege of some cities and withdraw back."

He also called for the creation of secure humanitarian corridors to allow the delivery of aid to the Libyan people.

Rebels in Benghazi are using fishing vessels and tugboats to send food, medicine and military supplies -- including weapons, ammunition and men -- to help defend the city.

Meanwhile, a ship chartered by the UN World Food Programme arrived in Misrata carrying 600 tonnes of foodstuffs that the WFP said could feed more than 40,000 people for a month.

And a rebel spokesman there said a French ship had arrived carrying medical aid.

Media watchdog Reporters Without Borders meanwhile said it has learned "from a reliable source" that four journalists -- a South African, two Americans and a Spaniard -- have been missing in eastern Libya since April 4.

The organisation also said it was "outraged" by the deportation of 26 foreign journalists by Libya on the grounds that their visas had expired.