Rebels claimed they had captured the strategic oil hub of Brega in eastern Libya on Saturday, a day after saying they had seized two other key towns in their push to close in on Tripoli.
In another blow to Moamer Kadhafi, the rebels also said that former prime minister Abdessalam Jalloud, who fell out of favour with the Libyan strongman in the mid-1990s but remains a highly popular figure, had defected and joined their ranks.
"The industrial zone is under our control, all Brega is now under our control," the top-ranking rebel official said on condition of anonymity, a day after rebels said had seized the coastal western towns of Zawiyah and Zliten.
"Kadhafi forces are withdrawing to the west, toward Bishr," the official said.
Jalloud "has gone to Benghazi yesterday night (Friday)," rebel spokesman Juma Ibrahim told reporters Saturday. "I don't know who he met there. He left by car," he added. Interview: Meet the Belfast teen who kills Kadhafi snipers
Overnight, rebel military commander Colonel Ahmed Omar Bani told AFP the ex-premier had managed to flee Tripoli and "has joined the rebels." Another source said his family accompanied him and they stopped first in Zintan.
His defection comes amid amid rumours that the Libyan strongman himself was preparing to flee as rebels appear to be closing in on the capital.
On Friday they claimed "Zawiyah is free" as they took up positions in its hospital hours after pounding the centre of the oil-refinery town, the last major barrier as they try to advance on Tripoli from the west.
The key refinery is the only source of fuel to the capital, and could leave it without critical supplies.
Insurgents also said they seized Zliten from Kadhafi's forces, hours after saying they were in the town's centre, 150 kilometres (93 miles) east of Tripoli.
"Zliten is now under the control of our fighters, but the fighting is not finished," the Information Centre For Misrata Military Council said, adding that 40-50 Kadhafi forces were dead and 12 African mercenaries captured.
Rebels have been seeking to sever Tripoli's supply lines from Tunisia to the west and to Kadhafi's hometown of Sirte in the east, hoping to cut off the capital, prompt defections and spark an uprising inside Tripoli.
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Meanwhile, a Tunisian defence ministry official said that Tunisian troops clashed with a group of armed Libyans overnight in southwest Tunisia.
An army patrol came under fire from armed men travelling aboard several 4X4 vehicles with Libyan registration plates in the Douz region, the official said on Saturday.
No one was caught and the attackers were still being hunted Saturday by ground and air forces, the official said, adding there were no casualties on the Tunisian side.
Jalloud was a member of the officers who grabbed power with Kadhafi in 1969 and was long considered the regime's second-in-command before being gradually sidelined in the 1990s.
A prime minister during the 1970s, Jalloud -- who has remained a popular figure in Libya -- had retired from politics following his dispute with Kadhafi and lived under hour arrest.
Libya's Awalam television channel quoted the former premier on its news ticker as saying: "Kadhafi's regime is finished."
With the rebels vowing to take Tripoli before the Muslim holy fasting month of Ramadan ends in late August, Italian Foreign Minister Franco Frattini urged the population of the capital to rise up against Kadhafi.
"We hope the people of Tripoli... understand the regime has harmed its own people and will therefore join a process of political change to cut off room for manoeuvre for Kadhafi's regime," Frattini said.
Meanwhile, the International Organisation for Migration said it was drawing up plans to evacuate thousands of migrants stranded in Tripoli because exit points have been cut off after a spate of rebel successes.
"There are already thousands of Egyptians who are ready for evacuation now, and what we are hearing is that every day there are more and more requests," IOM spokeswoman Jemini Pandya said.
For its part, the International Committee of the Red Cross reported a "rapid deterioration in the humanitarian situation" in several Libyan towns.
Meanwhile NATO, in its operational update for Friday, said it had hit targets in the vicinity of Tripoli, Zawiyah and Zliten, including nine military facilities around the capital.
Reports from Brasilia also said that clashes broke out late Friday at the Libyan embassy in the Brazilian capital between supporters of Kadhafi and his opponents.
Advocacy group Human Rights Watch meanwhile announced in a statement it had sent a "four-person team" to Tripoli and other sites in western Libya under government control, where "they engaged senior Libyan officials on human rights in the conflict and visited sites of NATO air strikes where civilians are alleged to have died."