A band of around 150 fighters loyal to deceased former Libyan leader Muammar Gaddafi have seized the town of Bani Walid, according to reports.
The diehard supporters launched a brazen attack on a base in Gaddafi's one-time stronghold, killing at least five people according to the AFP news agency.
One local official said that the loyalists had taken "the entire city of Bani Walid" according to Al Arabiya News.
The desert oasis town is located about 170km south of Tripoli.
The attack was made during daylight, according to reports, and was the first offensive launched by Gaddafi forces since the dictator's death on 23 October.
Mahmud Warfelli, a spokesman of the Bani Walid council, told AFP that he feared a "massacre" if the governing National Transitional Council did not intervene.
“There are around 100 and 150 men armed with heavy weapons who are attacking," the National Post quoted Warfelli as saying. We have asked for the army to intervene, but the defence ministry and NTC have let us down,” he said.
The attackers are said to be flying the green flags of the Gaddafi regime, and distributed leaflets vowing to "take the rats out".
On Saturday it was reported that protesters attacked an NTC base with home-made grendades over frustrations at being left out of the political process.
British Airways announced on Monday that they would resume flights to Tripoli, a reflection of what had been widely seen as growing peace and prosperity in the North African country.