Libyan interim government forces recaptured the airport in Sirte, Muammar Gaddafi's birthplace, on Thursday, amid mounting concern for civilians trapped inside the besieged city.

National Transitional Council (NTC) fighters took full control of Sirte airport, witnesses said. They had taken it two weeks ago, but then lost it again. Sirte's pro-Gaddafi defenders have used sniper, rocket and artillery fire to fight off two full-scale NTC assaults on the city in the past week.

Each side has accused the other of endangering civilians.

"They're shelling constantly. There's indiscriminate fire within individual neighborhoods and from one area to another," Hassan, a resident who escaped the city, told the media.

Civilians have been fleeing Sirte, a coastal city of 100,000 that is also under NATO aerial attack, and Libyan authorities have asked the United Nations for fuel for ambulances to evacuate wounded, a U.N. source in Libya said.

The United Nations is sending trucks of clean drinking water for civilians crammed into vehicles leaving Sirte for Benghazi in the west or Misrata in the east, the source said.

But fighting has prevented U.N. aid workers from reaching Sirte and Bani Walid, another town held by Gaddafi loyalists.

"There are two places we'd really like access to, Sirte and Ben Walid, because of concern on the impact of conflict on the civilian population," the source told Reuters in Geneva.

U.N. officials do not have any direct contact with pro-Gaddafi forces holed up in Sirte, where both sides accuse the other of cutting off water and electricity, he said.

Aid agencies said on Wednesday that a humanitarian disaster loomed in Sirte amid rising casualties and shrinking supplies of water, electricity and food.

Fighting on Sirte's eastern and western approaches was less intense on Thursday than on previous days, but the NTC said it had cleared a route between the two fronts, allowing its forces to link up, a strategic boost along with retaking the airport.

Interpol alert

More than a month after NTC fighters captured the capital Tripoli, Gaddafi remains on the run, trying to rally resistance to those who ended his 42-year rule, although some of his family members have taken refuge in neighboring Algeria and Niger.

Interpol issued an alert calling for the arrest of Gaddafi's son Saadi who fled to Niger three weeks ago. The Lyon-based police agency said it was acting at the request of the NTC, which accuses Saadi of leading military units responsible for crackdowns on protests and of misappropriating property.

Interpol has already issued ‘red notices’ for the arrest of Gaddafi, his son Saif al-Islam and his intelligence chief Abdullah al-Senussi, all wanted for the International Criminal Court for alleged crimes against humanity.

Gaddafi's former prime minister, Al-Baghdadi Ali al-Mahmoudi, who had fled to Tunisia, only to be arrested for illegal entry, has started a hunger strike in prison to protest a Libyan request for his extradition, his lawyer said.

Tunisian prosecutors say Mahmoudi will stay in jail pending an extradition decision, even though he won an appeal against a six-month prison sentence for entering Tunisia illegally.

Libya's new rulers are trying to get a grip on the whole country, rein in their own unruly militias and get on with reconstruction and democratic reform.

U.S. Senator John McCain, visiting Tripoli, said Gaddafi's overthrow had set an example to people all over the world, adding that U.S. investors were keen to do business with oil-exporting Libya once fighting there had stopped.

"We believe very strongly that the people of Libya today are inspiring the people in Tehran, in Damascus, and even in Beijing and Moscow. They continue to inspire the world, and let people know that even the worst dictators can be overthrown and be replaced by freedom and democracy," he told a news conference.