Government forces who for weeks were pinned down by artillery and rocket fire on the eastern edges of Sirte were able to advance several km (miles) into the city, capturing the southern district of Bouhadi.

A Red Cross convoy delivered oxygen and other urgently needed medical supplies to the Ibn Sina hospital on Monday after an earlier attempt was aborted because of heavy fighting.

"The situation on the ground was very tense with ongoing fighting," Red Cross delegate Hichem Khadraoui said.

"Under such conditions, we had to limit ourselves - after obtaining clearances from all the parties concerned - to bringing in the most urgently needed humanitarian aid."

Aid agencies say they are concerned about the welfare of civilians inside Sirte, one of the last pro-Gaddafi bastions left in the country, who are trapped by the fighting and running out of food, water, fuel and medical supplies.

Concerns about the humanitarian crisis have focused on the Ibn Sina hospital. Medical workers who fled Sirte say patients were dying on the operating table because there was no oxygen and no fuel for the hospital's generators.

Medical staff outside Sirte who had treated wounded civilians fleeing the fighting said they had been told the corridors were full of patients and that treatment was being given only to pro-Gaddafi fighters or members of his tribe.

A military spokesman for the interim government, the National Transitional Council (NTC), told a television channel that Gaddafi's son Mutassim was hiding in the Ibn Sina hospital.

"Our revolutionaries (in Sirte) are fighting those who are accomplices of the tyrant in crimes against the Libyan people," Ahmed Bani told Doha-based Libya TV.

"They are a group of killers and mercenaries led by Mutassim Gaddafi who is now in the Ibn Sina hospital in Sirte to avoid being hit, according to newly received information."

NTC forces in the east of Sirte unleashed barrages of tank, artillery and anti-aircraft fire until after sundown. NATO aircraft flew overhead.

NTC Commanders said their fighters in Sirte were waging street battles with Gaddafi supporters in a residential area situated two km (1.2 miles) from the city centre.

"We are surrounding them from all sides. We have orders to call in from all fronts and use all kinds of weapons," said NTC fighter Saeed Hammad.

Medical workers at a field hospital near Sirte said four NTC fighters were killed and 39 others were wounded on Monday.

On the way in to Bouhadi, the streets were deserted apart from some burned-out cars and tank shell casings. Billboards which had shown images of Muammar Gaddafi were torn down.

In Tripoli, the man convicted of the 1988 bombing of a US-bound airline over the Scottish town of Lockerbie told Reuters in an interview his role had been "exaggerated" and that the truth behind the bombing would emerge soon.

Abdel Basset al-Megrahi, the only person convicted in the bombing, said the facts of the case might be known soon. Convicted in a Scottish court, he was released two years ago on the grounds that he was suffering from terminal cancer.

Libyans ended Gaddafi's 42-year rule in August when rebel fighters stormed the capital. Gaddafi and several of his sons are still at large and his supporters hold Sirte and the town of Bani Walid, south of Tripoli.

De facto Prime Minister Mahmoud Jibril said on Monday the NTC would set in motion the process of democratic elections once Sirte was captured, instead of waiting until the whole country is under their control.

Jibril told a news conference in the city of Benghazi: "Bani Walid would be dealt with as a renegade region."

A city of about 75,000 people, Sirte holds symbolic importance. Gaddafi transformed his birthplace from a sleepy fishing town into Libya's second capital.

At his instigation, parliament often sat in Sirte and he hosted international summits at the Ouagadougou Hall, a marble-clad conference centre he had built in the south of the city.

Gaddafi's supporters are too weak to regain power, but their resistance is frustrating the new rulers' efforts to start building the post-Gaddafi Libya.