|Libyan rebels on armoured vehicles as they prepare to make their assault on Sirte [EPA]
Libya's National Transitional Council (NTC) has called for a united front against the remaining forces of Muammar Gaddafi on a day when the former dictator's son was intercepted while fleeing the country and the leader of his external spy service was arrested.
Al Jazeera correspondent Yvonne Ndege in Agadez, Niger, was told by security sources that a convoy of eight or nine vehicles were stopped while passing through the desert that separates the two countries.
"The vehicles were intercepted by Niger's authorities and it was found that Gaddafi's son Saadi Gaddafi and other senior officials were onboard the convoy," said Ndege.
The report was also confirmed by Amadou Morou, Niger's government spokesman and also its minister of justice.
"At this moment the convoy is en route to Agadez [northern Niger]. The convoy could arrive in Niamey [the capital] between now and tomorrow," he added.
Saadi, 38, the third of Kadhafi's seven sons, is regarded as a playboy who renounced a football career in 2004 to join the army, where he led an elite unit.
Separately on Sunday, Bouzaid Dorda, the head of Gaddafi's external security organisation, was arrested in Tripoli.
Dorda, a former prime minister, will be handed over to the NTC later on Sunday, an anti-Gaddafi fighter said.
He is one of several former government officials rounded up since Tripoli fell last month.
Gaddafi's foreign minister, Abdelati Obeidi, was arrested on August 31 in a suburb west of Tripoli.
Gaddafi himself remains on the run and a handful of towns in Libya remain under the control of his followers.
NTC fighters had given holdout towns a deadline of Saturday to surrender, and have been fighting since Friday inside the town of Bani Walid.
The deputy head of the NTC, meanwhile, told reporters in Tripoli that an interim administration will be formed within 10 days.
"A new government will be formed within one week to ten days," said Mahmoud Jibril, who serves as NTC "prime minister".
Jibril also called all of the forces fighting against Gaddafi to come "under the umbrella of the NTC".
Jibril added: "Negotiations with other brigades across Libya are still ongoing and they are going well. This is to legitimise the only legitimate government of Libya."
Reporting from Tripoli after Jabril's speech, Al Jazeera's correspondent Hashem Ahelbarra described the decision to bring all the military councils under the authority of the NTC as a "turning point" but added that it could lead to divisions between the political and military branches of the new government.
"The military council rejects the idea of joining the NTC and they are considering this move an attack to hijack their revolution and [weaken] their authority. They say they are the ones who have been fighting Colonel Gaddafi for six months, and they are the ones who should represent the wish of the Libyan people," Ahelbarra said.
He continued: "Sources from the military council told Al Jazeera that they reject the move and they will now ask for Mahmoud Jibril to quit. This is quite significant, it shows that differences and divisions are beginning to emerge."
Earlier on Sunday the NTC said their fighters were holding back an assault on one of the last bastions loyal to Gaddafi after fighting their way into the town and finding civilians in peril.
They said they were meeting stiff resistance in the town 150km southeast of the capital and were also edging towards the ousted ruler's birthplace Sirte.
"We are inside Bani Walid, we control big chunks of the city. There are still pockets of resistance," a fighter named Sabhil Warfalli said as he drove away from the front line.
NTC spokesman Ahmed Bani told reporters the plan for Bani Walid for now was to wait.
"When our forces entered Bani Walid they found the brigades of Gaddafi using citizens as shields," he told reporters. "We entered to prove that we can, and saw with our own eyes, Grad missiles over the roofs and they were using civilians."
"There are houses full of families and they are just standing outside that house, and also missiles over that house, so we are unable to strike the house because we know there are civilians inside. Also NATO can do nothing. So we prefer to return and surround Bani Walid until the young men inside have a solution," he said.
According to Warfalli, pro-Gaddafi forces were now concentrated in the central market area. This account was backed up by a resident named Khalifa Telisi who had telephoned a family in the town.
"There is still resistance from the central market. All other parts of Bani Walid have been liberated," Telisi said.
Cut in two
Inside the town, a pro-Gaddafi local radio station appealed for the city's 100,000 people to fight to the death.
"We urge the people of Bani Walid to defend the city against the rats and armed gangs. Don't back down. Fight to the death. We are waiting for you. You are just a bunch of gangsters. God is on our side," an announcer said.
Jalil al-Galal, an NTC spokesman in Tripoli, said resistance from Gaddafi fighters firing rockets and mortars inside the town had been "ferocious". Nevertheless, NTC spokesman Bani predicted council forces would have total control of Libya by the end of this month.
Gaddafi's loyalists also control Sirte, which sits on the main east-west coastal highway, effectively cutting Libya in two. Advancing NTC troops said the front line was now about 90km east of the city.
Fighters were firing tanks and howitzers amid the sound of heavy machine-gun fire and the roar of NATO warplanes overhead.
"There were clashes this morning and Gaddafi forces were firing Grad rockets, but we managed to advance a little bit and we will enter Sirte very soon," fighter Salah al-Shaery said.