* NTC forces mass in square near centre of Sirte
* NATO planes roar overhead, big explosions in town
* Gaddafi loyalists respond with rockets, snipers
By Alexander Dziadosz
SIRTE, Sept 24 (Reuters) - Libyan provisional government forces backed by NATO warplanes swarmed into the city of Sirte on Saturday but weathered heavy sniper fire as they tried to win control of one of deposed leader Muammar Gaddafi’s last bastions of support.
Black smoke billowed over the town as National Transitional Council (NTC) forces massed in Zafran Square about 1 km (half a mile) from the town centre. Gunfire could be heard from the centre as NTC fighters moved tanks and mortars into the square.
Pick-up trucks mounted with machineguns and loaded with NTC fighters raced into the town. NTC forces also advanced from the south of Sirte, Gaddafi’s hometown on the Mediterranean coast.
“They have snipers above the mosques, above the buildings. They’re using the houses and public buildings,” NTC fighter El-Tohamy Abuzein told Reuters from his position in Zafran Square.
NATO, whose war planes played a vital role in the six-month that toppled Gaddafi, would not comment on its operations in Sirte on Saturday. Its planes hit a number of targets on Friday, including an ammunition depot and an anti-aircraft gun.
A large cloud of smoke over the town was the result of a strike on an ammunition dump, NTC fighters said. At the western gate, gunners fired artillery towards the town and both sides exchanged volleys of rockets.
Previously, NTC forces have retreated from Sirte and the other final Gaddafi stronghold, Bani Walid, after poorly organised assaults met fierce resistance from loyalists.
Though NTC forces have in recent days tightened their grip on many southern oasis towns which sided with Gaddafi, that progress has been overshadowed by unsuccessful efforts to take the last strongholds.
NTC commanders say their advance on Sirte has been hampered by the presence of large numbers of civilians, many of whom have fled in the past week.
A Gaddafi spokesman has accused NATO of killing several hundred civilians with its strikes on the town. Communications have been largely cut off since the fall of the capital Tripoli last month.
Taking Sirte would be a huge boost for the NTC as it tries to establish credibility and a devastating blow for Gaddafi, who is still believed to be on the run inside Libya.
On Thursday, the NTC said it had taken full control of another major hold-out, Sabha, which was the traditional base for Gaddafi’s own tribe. About 800 km (500 miles) south of Tripoli, it had been occupied by fighters loyal to him.
The NTC says it also controls Jufra, to the northeast of Sabha, and the nearby oasis towns of Sokna, Waddan, and Houn.
The manhunt for Gaddafi, who has been in hiding for weeks occasionally issuing audio messages through Syrian-based Arrai TV, is drawing closer to its target, NTC officials say.
The network broadcast an audio message from Gaddafi’s daughter Aisha on Friday. It was the first time she had spoken publicly since fleeing into exile in Algeria last month along with two of his sons.
“I reassure you about your leader, oh Libyans,” the 35-year-old lawyer said, sounding distressed. “He is well and thank God his spirits are high. He is carrying his weapon and fighting along with his sons at the fronts.
North of Bani Walid, NTC military forces brought forward tanks and Grad rocket launchers for a renewed attempt to take the town although it was not clear when the attack might begin.
The offensive there has been frustrated by stiff resistance from well-drilled loyalist fighters and also a lack of organisation among the attacking forces.
They operate in disparate units based on their home towns, with little overall command.
“We don’t take orders from the NTC. We listen only to our own commander,” said Ziyad Al Khemri, a fighter from Zawiyah, just west of Tripoli.
The NTC, the political leadership of the rebel movement which rose up against Gaddafi’s 42-year-rule and drove him from power with support from the West and several Arab nations, faces a challenge in trying to impose its authority across the nation.
It said last week it would move to Tripoli only after its forces were in full control of Libyan territory, contradicting an earlier pledge to move the interim administration from eastern Banghazi around mid-September.
Libya’s de facto president, Mustafa Abdel Jalil, was due to hold a news conference in Benghazi on Saturday afternoon, where he will face questions on the make-up of a new cabinet and how to demobilize and disarm former rebel fighters.
Reporting by Goran Tomasevic south of Sirte, Sherine El Madany east of Sirte, William Maclean and Joseph Logan in Tripoli, John O'Donnell in Brussels, Barry Malone in Tunis, Ahmed Tolba in Cairo and Joseph Nasr in Berlin; Writing by Barry Malone