Muammar Gaddafi's presidential guard has surrendered to Libya's rebels, Al Arabiya reported on Sunday, citing the rebel National Transitional Council.
Al Jazeera television also reported that troops responsible for the veteran leader's security had laid down their arms.
The head of the rebel National Transitional Council also told Al Jazeera television that Libya's rebels have captured Muammar Gaddafi's son, Saif Al-Islam.
"We have confirmed information that our guys have captured Saif Al-Islam," Mustapha Abd El Jalil said. "We have given instructions to treat him well so that he can face trial."
Separately, Britain said that the end was approaching for Gaddafi as rebels advanced into the capital Tripoli and called on him to step aside to spare his people further bloodshed.
"It is clear from the scenes we are witnessing in Tripoli that the end is near for Gaddafi," the prime minister's office said in a statement.
"He has committed appalling crimes against the people of Libya and he must go now to avoid any further suffering for his own people," it added.
Earlier, Gaddafi urged Libyans to take up arms and crush the uprising in Tripoli as rebel troops streamed toward the capital on Sunday for a final onslaught on his stronghold.
"I am afraid if we don't act, they will burn Tripoli," he said in an audio address broadcast on state television. "There will be no more water, food, electricity or freedom."
Thousands of rebel fighters advanced to within 20 km (12 miles) west of the centre of Tripoli on Sunday evening in an effort to join fighters already inside the city, a Reuters witness said. Another group of 200 rebels reached Tripoli by boat from Misrata to the east, an activist in Tripoli said.
In a coordinated revolt that rebels have been secretly planning for months to end Gaddafi's 41-year rule, shooting started on Saturday night across Tripoli moments after Muslim clerics, using the loudspeakers of mosque minarets, called people on to the streets.
The fighting inside Tripoli, combined with rebel advances to the outskirts of the city, appeared to signal the decisive phase in a six-month conflict that has become the bloodiest of the "Arab Spring" uprisings and embroiled NATO powers.
Gaddafi, in his second audio broadcast in 24 hours, dismissed the rebels as rats.
"I am giving the order to open the weapons stockpiles," Gaddafi said. "I call on all Libyans to join this fight. Those who are afraid, give your weapons to your mothers or sisters.
"Go out, I am with you until the end. I am in Tripoli. We will ... win."
A Libyan government official told Reuters that 376 people on both sides of the conflict were killed in fighting overnight on Saturday in Tripoli, with about 1,000 others wounded.
"Gaddafi's chances for a safe exit are diminishing by the hour," said Ashour Shamis, a Libyan opposition activist and editor based in Britain.
But Gaddafi's fall, after four decades in power, is far from certain. His security forces did not buckle, and the city is much bigger than anything the mostly amateur anti-Gaddafi fighters, with their scavenged weapons and mismatched uniforms, have ever tackled.
If the Libyan leader is forced from power, there are question marks over whether the opposition can restore stability in this oil exporting country. The rebels' own ranks have been racked by disputes and rivalry.
Rebels said after a night of heavy fighting they controlled a handful of city neighbourhoods. Whether they hold on could depend on the speed with which the other rebels reach Tripoli.
"The rebels may have risen too early in Tripoli and the result could be a lot of messy fighting," said Oliver Miles, a former British ambassador to Libya. "The regime may not have collapsed in the city to quite the extent they think it has."
But the rebel advance towards the city was rapid, and there was no sign of fierce resistance from Gaddafi's security forces. In the past 48 hours, the rebels west of Tripoli have advanced about 30 km, halving the distance between them and the capital.
Government forces put up a brief fight at the village of Al-Maya, leaving behind a burned-out tank and cars that had been torched. "I am very happy," said one resident.
Anti-Gaddafi fighters streaming through paused long enough to daub graffiti on walls in the village. One read "We are here and we are fighting Gaddafi," another "God is great." They then moved on towards Tripoli.
In Benghazi, the eastern Libyan city where the anti-Gaddafi revolt started and where the rebels have their main stronghold, a senior official said everything was going according to plan.
"Our revolutionaries are controlling several neighbourhoods and others are coming in from outside the city to join their brothers at this time," Abdel Hafiz Ghoga, vice-chairman of the rebel National Transition Council, told Reuters.
A spokesman for Gaddafi, in a briefing for foreign reporters, underlined the message of defiance.
The armed units defending Tripoli from the rebels "wholeheartedly believe that if this city is captured the blood will run everywhere so they may as well fight to the end", said spokesman Moussa Ibrahim.
"We hold Mr Obama, Mr Cameron and Mr Sarkozy morally responsible for every single unnecessary death that takes place in this country," he said.
A diplomatic source in Paris, where the government has closely backed the rebels, said underground rebel cells in the capital had been following detailed plans drawn up months ago and had been waiting for a signal to act.
That signal was "iftar" -- the moment when Muslims observing the holy months of Ramadan break their daily fast. It was at this moment that imams started broadcasting their message from the mosques, residents said.
But the overnight fighting inside the city, while fierce, was not decisive. Rebels said they controlled all or parts of the Tajourah, Fashloom and Souk al-Jumaa neighourhoods, yet there was no city-wide rebellion.
In Tripoli on Sunday, the two sides appeared to be jockeying for control of roof terraces to use as firing positions, possibly in preparation for a new burst of fighting after dark.
A rebel activist in the city said pro-Gaddafi forces had put snipers on the rooftops of buildings around Bab al-Aziziyah, Gaddafi's compound, and on the top of a nearby water tower.
As he spoke, single gunshots could be heard in the background, at intervals of a few seconds.
"Gaddafi's forces are getting reinforcements to comb the capital," said the activist, who spoke by telephone to a Reuters reporter outside Libya.
"Residents are crying, seeking help. One resident was martyred, many were wounded," he said. It was not immediately possible to verify his account independently.For all the latest business news from the UAE and Gulf countries, follow us on Twitter and Linkedin, like us on Facebook and subscribe to our YouTube page, which is updated daily.
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