However, an NTC spokesman in Benghazi said that the new authorities would not complete their transfer to the traditional capital until Libya was "fully liberated."
"We still have work to do here" in Benghazi, said Fathi Baja, head of the NTC's political affairs committee.
Meanwhile, Kadhafi's sole remaining media mouthpiece, Mishan al-Juburi, owner of the Syria-based Arrai Oruba television, said the defeated leader and his son Seif al-Islam were still in Libya.
"I can tell you that I spoke with Kadhafi very recently," Juburi told AFP.
"He is in Libya, in very good spirits, feels strong, is not afraid, and would be happy to die fighting against the occupiers," Juburi, a former Iraqi MP, said by telephone.
"His son Seif al-Islam is in the same state of mind," added Juburi, whose channel has broadcast a number of audio messages from the Kadhafis since Tripoli was overrun by rebel fighters last month.
Libya's new rulers are anxious to arrest Kadhafi and put him on trial, sealing their hold on the country.
They are fearful he may slip into a neighbouring state, particularly Niger, to which a convoy carrying other senior ousted regime officials fled on Monday.
Bidding to cut off Kadhafi's potential escape routes, the NTC said it had dispatched a team to Niamey.
"We have sent a delegation today that is going to Niger to talk... about securing our borders to stop any kind of infiltration," said Baha.
"We ask any neighbouring countries to stop Kadhafi people from going to their land," Fathi told reporters in Benghazi.
The United States said Kadhafi aides who entered Niger were being detained.
"Our understanding is that the convoy included some military and senior officials under Kadhafi's former regime," State Department spokeswoman Victoria Nuland said.
"They are now being held in the capital... and they are being monitored closely by Nigerien officials."
Washington, in addition to working with Niger, "is in contact with Mali, Mauritania, Chad and Burkina Faso to emphasise the importance of respecting the UN Security Council resolutions and of securing their borders," Nuland said.
The United States was "calling on all of these countries to make every effort to control their borders, to detain any Kadhafi regime officials, to confiscate contraband and any illegal weapons, to disarm them and also to confiscate any wealth that might properly belong to the Libyan people."
The large convoy of civilian and military vehicles entered Niger late on Monday.
Niger was adamant Kadhafi was not with them, and Washington said he was not believed to be among them.
Kadhafi's remaining forces have been a given a Saturday deadline to surrender, in a bid to spare further bloodshed.
At Bani Walid, 170 kilometres (105 miles) southeast of Tripoli, negotiators were still seeking to broker the oasis town's peaceful surrender.
"The negotiations were successful yesterday and we are waiting for the NTC to give us the green light to go in," said the council's chief negotiator, Abdullah Kenshil.
He also said Seif al-Islam was still in the Bani Walid area. "He has been sighted but he's going in and out (of town)... Because he has left the town, it doesn't mean he has left the area."
NTC leaders say they are committed to avoiding bloodshed in Bani Walid, even after a delegation sent there on Tuesday retreated after being fired on.
"The elders have joined the revolution," Kenshil said, adding that some were in Tripoli and others back in Bani Walid after armed men loyal to Kadhafi initially prevented them from returning.
In the hamlet of Wishtata, some 40 kilometres (25 miles) from the front, Colonel Abdullah Abu Asara said his volunteer fighters were ready for anything.
"We are fully ready to attack, we are just waiting for the command from the National Transitional Council, we are under their command now," he told AFP.
NTC forces on Wednesday advanced along the road from Um Khunfis to the Red Valley, the pro-Kadhafi forces' frontline, some 60 kilometres (40 miles) east of Sirte, an AFP journalist said, reporting artillery fire.
NATO, in its latest operational update on Wednesday, said its warplanes had bombed six tanks, six armoured fighting vehicles, four armed vehicles, a munitions store and an artillery piece in Sirte the previous day.
Libyan oil exports are unlikely to return to their pre-war level before 2013, the new head of the International Energy Agency said.
"Our experts think that 2013 or beyond will most probably show the complete full restoration of the Libyan supply to the market, but not before that," Maria van der Hoeven told AFP in an interview.
"Stabilising the political situation is the first thing that has to be done," he said.
Libya produced about 1.6 million barrels per day (bpd) before the rebellion against Kadhafi broke out in mid-February.
Just how quickly Libyan oil will return to the market remains one of the key questions of the post-Kadhafi era, not only for consumer nations but also for Libya's new rulers who badly need oil export revenue to fund reconstruction.