BIR AL-GHANAM, Libya - Libyan rebels who seized this town 80 km (50 miles) south of Tripoli said on Monday they would now push on towards Muammar Gaddafi's stronghold in the capital.

This small settlement in the desert is the closest rebel position to Tripoli and its capture at the weekend is likely to give new hope to a faltering six-month campaign to oust Gaddafi.

Anti-Gaddafi fighters had been camped since late June on the outskirts of Bir al-Ghanam, unable to advance. According to rebels in the town on Monday, they moved in on Saturday under cover from NATO warplanes.

They said their next target was Zawiyah, a town on the Mediterranean coast 50 km west of Tripoli.

Zawiyah was the scene of two failed uprisings against Gaddafi's rule since February. Many of the fighters in Bir al-Ghanam are from there, although a number of those who took part in the uprisings are now in prison or dead.

"Our aim is to get to Zawiyah. Once we do that Gaddafi is finished," said rebel fighter Murad Bada, who was sitting under the shade of a tree and humming a song about Zawiyah.

The capture of Bir al-Ghanam is the biggest rebel breakthrough in weeks of largely static fighting on three fronts across Libya.

But that alone is not enough to undermine Gaddafi's grip on power.

The small rebel force approaching from the south could face much stiffer resistance as it draws nearer to the capital, where his troops are likely to put up a more fierce fight and he can can count on a certain level of popular support.

The rebel advance elsewhere has been hampered by divisions and infighting, as well as a lack of experience in warfare.

Libya's prime minister told reporters in Tripoli on Sunday that government forces were in control of Bir al-Ghanam after fighting off a rebel attack.

But in the town early on Monday, the only sign of government forces was the weaponry they had left behind when they fled, said a Reuters reporter in the town centre.

One artillery piece was abandoned, and three tanks were burned out. Next to one tank -- still mounted on the trailer of a tank transporter -- was a deep crater which appeared to have been caused by a NATO air strike.

Rebel fighters were resting in the heat. One was wrapping a wound on his arm which he said was caused by rocket shrapnel.

Another fighter, 32-year-old Salim Shawsh, said in the five-hour battle on Saturday to take Bir al-Ghanam, rebels attacked on foot from behind ridges on the outskirts of the town, with NATO air support.  

He said five rebel fighters were killed, including a Libyan-American father and son, part of a large contingent of foreigners with Libyan roots who have come back to fight against Gaddafi.

The pair was hit by rocket fire and they died with the father clutching the son, Shawsh said.