People stand around bones found at a mass grave in Tripoli September 25, 2011.[Photo/Agencies]

To the east of Tripoli, NATO bombers hit the city of Sirte to clear the way for fighters with the National Transitional Council (NTC) who are trying to capture Gadhafi's hometown.

But Gadhafi loyalists showed they were still a threat by attacking the desert oasis town of Ghadames, on the border with Algeria, NTC officials said. ?

The mass grave was the first physical evidence revealed so far of the Abu Salim prison massacre, an event that was covered up for years but created simmering anger that ultimately helped bring about Gadhafi's downfall.

"I am happy this revolution succeeded, and that our country will be better," said 45-year old Sami al-Saadi, who believed two of his brothers died in the massacre. "But when I stand here, I remember my brothers who were killed."

According to accounts from survivors who have spoken to human rights groups, starting at dawn on June 29, 1996, guards lined up inmates in the courtyards of the Abu Salim prison.

Security men, standing on the prison rooftops, fired at the inmates with Kalashnikov rifles before using pistols at close range to finish them off.

The uprising that toppled Gadhafi was ignited by protests linked to the Abu Salim massacre. In February, families of inmates killed there demonstrated in the eastern city of Benghazi to demand the release of their lawyer. ?

Nato jets

Anti-Gadhafi forces had pushed to within a few hundred metres of the centre of Sirte, one of the last bastions of pro-Gadhafi resistance in Libya, but later drew back to let the NATO jets do their work.

"Yesterday our freedom fighters attacked Sirte city from two sides. That doesn't mean that Sirte is free now, but it is an indication that Sirte will be free soon," said Ahmed Bani, NTC military spokesman in Tripoli. ?

"I'm asking now any militiamen fighting on the side of the tyrant (to realise) that the game is over."

On Sunday, the roar of jet engines could be heard overhead, as well as sporadic booms when NATO ordnance hit targets on the ground. One strike, giving off a deep thud, released a big cloud of smoke and dust over the south of the city.

There was little fighting on the ground west of Sirte, where NTC fighters have advanced closest to the city centre.

On the eastern side, the forces pushed to within 15 km (9 miles), an advance of more than 25 km. A Reuters reporter there said the NTC forces had been helped by heavy NATO bombing. ?

She said she could hear the sound of artillery fire and see black smoke on the horizon. Doctors at a hospital east of Sirte said one fighter had been killed and 12 wounded in clashes on Sunday.

Taking Sirte would be a huge boost for the NTC as it tries to establish credibility as a government able to unite Libya's fractious tribes and regions, and a blow for Gadhafi, widely believed to be on the run inside Libya.

Offering what may be a glimpse into the deposed leader's state of mind, his spokesman contacted Reuters to deny reports that Gadhafi and his family had helped themselves to Libya's oil wealth. ?

"The leader of the revolution and his family are among the poorest citizens," said the spokesman, Moussa Ibrahim. He spoke by telephone and did not reveal from where he was calling. ?

Accounts from NTC fighters and people who had left Sirte indicated pro-Gadhafi forces were trying to prevent civilians from fleeing, effectively using them as human shields.

"Gadhafi's forces have surrounded the area, closed it off, by shooting at people," said a man called Youssef, who was driving away from Sirte with his wife. "There are a lot of people who want to get out but can't."

A man who said he was a doctor at a hospital in the centre of Sirte said by telephone it was the NTC forces who were causing civilians to suffer.

He said wounded people were dying daily because medical supplies were running out and part of the hospital had been hit by shellfire.

The doctor, who gave his name as Abdullah Hmaid, spoke to Reuters using the mobile telephone of the Gadhafi spokesman, Ibrahim, who is a native of Sirte.

"The armed opposition refuses to cooperate with us and is imposing a health blockade on the city," said Hmaid.

"We call on the Word Health Organisation, the International Red Cross and Amnesty International and human rights organisations to work to break the siege of more than 200,000 people in Sirte."

Fragile grip

The attack by pro-Gadhafi forces on Ghadames underlined the fragility of the NTC's grip even on parts of the country nominally under its control.

The town, about 600 km south-west of Tripoli, is near a border crossing that pro-Gadhafi Libyans have used to flee into Algeria. Its old town, an intricate maze of mud walls, is listed as a UNESCO world heritage site.

"These militias have attacked our people in Ghadames city ... All the information we have got is that these groups are related to the son of Gadhafi, Khamis," the NTC's Bani told a news conference.

"Our freedom fighters have taken control of that area," he said, though he acknowledged the clashes were not completely over. "This problem will end soon. It's a matter of days."

A month after ousting Gadhafi's forces from Tripoli and most of the country, the NTC is now facing challenges to its rule from only two main locations, Sirte and Bani Walid, a town about 170 km (105 miles) south-east of Tripoli.

Until both are captured, Libya's new rulers say they cannot begin the process of holding the first elections. ?

That leaves the country in limbo where the only real authority comes from disparate factions of anti-Gadhafi fighters who are still armed and want a stake in the new Libya.

Deepening the uncertainty, the NTC has been unable to form a caretaker government because of wrangling over portfolios.

It could now miss the latest deadline it gave itself for naming a government, within the next few days, a source close to the council told Reuters.