Libya conflict: Heavy gunfire erupts in Tripoli
Explosions and sustained gunfire have been heard in parts of Tripoli, as rebels close in on the Libyan capital.
A credible source told the BBC there had been heavy fighting in some districts. A rebel official said the uprising had begun in Tripoli.
But Col Muammar Gaddafi said his forces had eliminated "rats". He accused the rebels of trying to destroy Libya.
The rebels earlier captured the city of Zlitan, 160km (100 miles) east of Tripoli, and Zawiya, 40km to the west.
However, pro-Gaddafi forces have been fighting back at the oil port of Brega, with the rebels admitting that they fell back from the eastern town's industrial zone under heavy bombardment.
There were reports of protests and gunfire in areas to the north and east of Tripoli, including the Tajoura district, where there was trouble at the start of this uprising against Col Gaddafi, the BBC's Matthew Price in the capital reports.
Abdel Hafiz Ghoga, vice-chairman of the rebel National Transition Council (NTC), was quoted as saying by Reuters news agency: "The zero hour has started. The rebels in Tripoli have risen up."
"There is co-ordination with the rebels in Tripoli. This was a pre-set plan," said Mr Ghoga.
But Col Gaddafi's Information Minister Moussa Ibrahim later put the trouble down to "small armed gangs".
"Tripoli is safe, and completely under the control of the armed people committees and the volunteers and the honourable people of Tripoli," the minister said.
"Some gunmen entered two or three areas of Tripoli. They were confronted and everything ended within half an hour."
In an audio broadcast shortly afterwards, Col Gaddafi congratulated his supporters for repelling the rebels.
"Those rats were attacked by the masses tonight and we eliminated them," he said.
The Libyan leader certainly has support in Tripoli, our correspondent says.
In recent weeks more and more checkpoints have sprung up across the city at night. Pro-Gaddafi men and women have received weapons training.
However, the momentum is clearly against Col Gaddafi and his supporters, our correspondent adds, with rebels having better weaponry.
A rebel military spokesman, Col Ahmed Bani, earlier confirmed that rebel forces had fallen back in Brega.
Brega, home to Libya's second-largest hydrocarbon complex and where oil from the country's main fields is refined, has repeatedly changed hands during the six-month-old conflict.
"Yesterday, the industrial zone was under our complete control, but the truth is that today the situation has changed due to heavy artillery shelling," Col Bani said on Saturday.
"We withdrew to the eastern part of the industrial zone."
After visiting Zlitan, the BBC's Orla Guerin said the rebels appeared to have a firm grip on the town, controlling the centre and manning checkpoints.
However, small-arms and mortar fire could still be heard, and rebels told the BBC that beyond a strategic bridge in the centre, there was still a risk of attack.
In Zawiya, the BBC's Rupert Wingfield-Hayes said the rebels had succeeded in pushing Col Gaddafi's forces out of the city and were now in complete control there.
The rebels burned Col Gaddafi's green flag and stamped on the pictures of the Libyan leader.
Our correspondent says the bodies of several pro-Gaddafi fighters were found. The rebels said they were mercenaries from neighbouring Chad.
Rebel forces have also moved towards Tripoli from the south.
Nato, enforcing a UN-mandated no-fly zone to protect civilians since March, controls sea access to Tripoli.
Meanwhile, reports suggest fresh senior figures in the Gaddafi camp may have defected:
- Abdel Salam Jalloud, who helped Col Gaddafi come to power in 1969 but fell out with him in the 1990s, is believed to be making his way to Europe from neighbouring Tunisia
- Libyan Oil Minister Omran Abukraa failed to return to Libya on Thursday after a visit to Italy and went to Tunisia instead, Tunisian sources said
Libya's conflict broke out in February, inspired by uprisings in Tunisia and Egypt which toppled the presidents of those countries.
Rebels in the east rapidly consolidated their gains, but a stalemate developed in the west as rebels there faced overwhelming military force.
The fighting has stranded thousands of migrant workers - many of them Egyptians - in Tripoli.
The International Organisation for Migration (IOM) said it was planning to evacuate them in the coming days.
Since the conflict in Libya began, an estimated 600,000 migrant workers have fled the country, many with the help of the IOM, but many remain.