Aid agencies in Sirte say they are concerned about the welfare of civilians inside the Libya's besieged city, the hometown of deposed leader Muammar Gaddafi, who are trapped by the fighting and running out of food, water, fuel and medical supplies.

The International Committee of the Red Cross (ICRC) took some supplies into Sirte last week, and it tried again on Monday, assembling a convoy of two trucks carrying aid, and accompanied by two four-wheel drive vehicles.

The convoy set off from a bridge a few kilometres west of Sirte but came to a halt after only about 100 metres because interim government forces started firing into the city.

They fired a heavy barrage of mortars, artillery, rocket-propelled grenades and anti-aircraft weapons just as the convoy was starting to move. The ICRC convoy turned around and headed back west, away from Sirte.

An anti-Gaddafi commander at the scene, Ismail Al-Sosi, told Reuters: "The rebels secured the way for the International Red Cross to go but as soon as they entered the city they returned because of the (pro-Gaddafi) militias firing. We did not start the firing. The militias started the firing."

However, a Reuters team who witnessed the incident said they saw no incoming fire from the Gaddafi loyalists inside Sirte.

Speaking just before the aborted attempt to get supplies into the city, an ICRC official said the humanitarian situation there was dire.

"We're trying to provide medical assistance and oxygen to the hospital in Sirte," said Hishem Khadrawy. "We are really concerned about the medical situation because of the conflict."

Civilians Trapped

Civilians who were able to get out of Sirte spoke of many other people unable to leave and facing deteriorating conditions.

Boshnab Khalifa drove out of the city with his family. A woman in the back seat of his car clutched a Koran.

"We were in our apartment and then the wall was blown in by a rocket," he said. "The situation is very bad. Our family and our friends are trapped inside. They cannot get out. There are many families trapped inside, some have no gas for their cars, other (cars) have been damaged or destroyed."

Another resident fleeing Sirte, Mohammed Diap, said pro-Gaddafi militias were barring people from getting out.

"There is no food, no water, no power. Some are trapped because there is no fuel, others are trapped because of the militias," he said. "The people who are trapped inside are in danger. There is random shelling everywhere."

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.

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.

A city of about 75,000 people, Sirte holds symbolic importance. Gaddafi, known for his self-aggrandising gestures, 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 on a desert plot in the south of the city.

Hospital Treatment

Concerns about the humanitarian crisis have focussed on the city's 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 on Monday 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 Gaddafi's tribe.

"There is a section for civilians and a section for the (pro-Gaddafi) brigades. They are only treating the brigades and leaving the normal people," one member of an ambulance crew told Reuters. That account was repeated by a doctor at a field hospital near the city.

Forces loyal to Libya's interim government, the National Transitional Council (NTC), have surrounded Sirte. They have until now made little inroads from their positions on the edge of the sprawling city.

On Monday though, pro-Gaddafi forces on the eastern side of Sirte appeared to have pulled back without a fight, allowing NTC fighters to advance about 4 km from their previous positions.

A Reuters reporter who moved in with them said she saw deserted neighbourhoods and empty houses, with burned-out cars in the streets. Sheep, with no one tending them, wandered down one street.

The NTC forces had capitalised on their advance by finding weapons which they said had been abandoned in civilian houses.

A group of fighters headed out of the city on foot carrying a haul of rocket-propelled grenades, Kalashnikov rifles, boxes of ammunition and pairs of new army boots.

"We took them from Muammar, Allahu Akbar! (God is Greatest)," one of the fighters shouted.