The head of Libya's interim authority Mustafa Abdel Jalil has appeared in the embattled city Sirte, say reports. Mr Jalil was greeted by cheering National Transitional Council (NTC) troops, firing weapons in celebration, said Reuters news agency. Sirte is the home town of fugitive leader Col Muammar Gaddafi and one of the last loyalist strongholds. The anti-Gaddafi forces have cornered the loyalists in a small area of the city but are facing stout resistance. Nato officials have said they are surprised that the pro-Gaddafi fighters are continuing to fight with such resilience in the city. The NTC says that once Sirte falls, they will declare Libya to be fully liberated. Nato's chief military officer Adm Giampaolo Di Paola said the loyalist forces were acting like a cornered, "ferocious beast". He said he was "surprised by their capacity to resist" but that they also had no other choice but to "fight until the end". Nato spokesman Roland Lavoie said that with NTC forces now in control of much of the city and supply lines to the loyalists cut off, "it just does not make sense" for them to still be fighting. "This could certainly be qualified as surprising both from a military and political point of view," as they "could not change or influence the outcome of this conflict". 'Tyres slashed' Since launching what they said would be their final offensive on Sirte on Friday, NTC forces - coming from both the east and west - have pushed the loyalists into a small area of land close to the sea. "There remains still 2 sq km (0.8 sq miles) to take to free the city completely," NTC commander Wissam bin Ahmid told the AFP news agency, adding that they were still facing sniper fire in the streets. "Our main worry are the families still in the city who are too afraid to leave their houses as the snipers are using them as firing posts." The anti-Gaddafi forces have captured many of the major facilities which being used as loyalist bases, including a conference centre and hospital. On Tuesday, they said they had captured a police headquarters after finding it deserted, AFP reported. The troops ransacked the building, said the agency, destroying images of Col Gaddafi, whose whereabouts are still unknown. Both sides are still sustaining losses, including at least one NTC fighter killed by so-called friendly fire. Thousands of people have fled Sirte in recent weeks but an unknown number of civilians are thought to have stayed behind - many are reported to have believed pro-Gaddafi warnings that they would be killed or captured by the NTC. The BBC's Wyre Davies, on the outskirts of Sirte, says a lull in fighting on Tuesday morning enabled hundreds more people to flee the city. "There are explosions all the time," one woman travelling in a car with seven children told Reuters news agency. "There is no water. There is nothing." Another man told AFP there had been 35 people in his house, mostly women, living on bread and rice for the past two months. "The Gaddafi forces prevented us from leaving, slashing the tyres of cars in garages and forcing us to turn back," he said. Cars leaving Sirte are being stopped and searched carefully at checkpoints, says our correspondent, over suspicions that pro-Gaddafi fighters are trying to pass themselves off as civilians to escape. The NTC troops are also preparing to mount an assault on Bani Walid, another Gaddafi stronghold further south in the desert. But Mr Lavoie said there was "no evidence of significant pro-Gaddafi presence or activity in the rest of the country". Nato is carrying out air strikes over Libya under a UN resolution to protect the civilian population. It has vowed to continue until the former regime no longer poses a threat. On Sunday, Secretary General Anders Fogh Rasmussen said the alliance was "pretty close to the very end of this operation".