Celebratory bursts of gunfire and fireworks lit up the skies over Tripoli early Thursday as word spread that Libyan government fighters had captured Moammar Gadhafi's son Mo'tassim in Sirte.

The capture of the deposed leader's national security adviser, and the first member of the Gadhafi family, is a big boost to Libya's new rulers whose forces are still battling pro-Gadhafi fighters in his home town of Sirte.

National Transitional Council officials told Reuters Mo'tassim was captured Wednesday after he tried to escape the battle-torn city in a car with a family.

He was arrested today in Sirte, Col. Abdullah Naker, head of the Tripoli Revolutionary Council, told Reuters. Other NTC sources said Mo'tassim was taken to Benghazi, where he was held and questioned at the Boatneh military camp. He was uninjured but exhausted.

As news of the capture spread, hundreds of people gathered in the capital's old city, singing, waving Libya's new flag and shouting God is greatest.

Ships sounded their whistles in the harbor and car drivers honked horns, many with passengers hanging from the windows.

Now we have one Gadhafi, shouted Mohammed, a 23-year-old engineer, who, despite it being banned in Libya, swigged from a bottle of alcohol with three friends. Soon we will have the old man Gadhafi and all the Gadhafis.

But fair trial, fair trial, said his friends.

One man hoisted a small girl on his shoulders, as men nearby unleashed volleys of gunfire into the air, sending some fleeing into doorways. Local reports said several people injured by celebratory gunfire were taken to hospital.

Look at this child, the man told Reuters in English. For her, there will be no memory of Gadhafi. He will be an old dream, just a bad dream. That is all.


Hundreds of NTC fighters took to the streets in other cities and fired into the air after Arab television channels broadcast news of the arrest.

Gadhafi loyalists have fought for weeks in Sirte, one of two major towns where they still have footholds, two months after rebels seized Tripoli.

But NTC fighters have made significant advances in Sirte in recent days. On Wednesday, they said they were fighting pro-Gadhafi fighters in two small areas.

Many people who study Libya believe Mo'tassim belongs to a conservative camp -- rooted in the military and security forces -- which resisted his brother Saif al-Islam's reform attempts.

A senior NTC military official told Reuters that Mo'tassim had cut his usually long hair to disguise himself.

Gadhafi and his most prominent son, Saif Al-Islam, have been on the run since the fall of Tripoli. Gadhafi is believed to be hiding somewhere far to the south in the vast Libyan desert.

His daughter Aisha, her brothers Hannibal and Mohammed, their mother Safi and several other family members fled to Algeria in August. Another son, Saadi, is in Niger.

Libyan prosecutor Abdullah Banoun said on Wednesday the NTC had given approval for an investigation to be opened into Saadi over his role in the 2005 murder of a soccer player.

NTC fighters in Sirte on Wednesday walked up the same battle-scarred streets strewn with empty ammunition cases where they had engaged in fierce clashes a day before. Other fighters searched houses as a few civilians emerged from basements.

More than 80 percent of Sirte is now under our control. Gadhafi's men are still in parts of the Number Two and the 'Dollar' neighborhoods, said NTC commander Mustah Hamza.

In the Number Two neighborhood, government forces found 25 corpses wrapped in plastic sheets. They accused pro-Gadhafi militias of carrying out execution-style killings.

Five corpses shown to a Reuters team wore civilian clothes and had their hands tied and gunshot wounds to the head.

Green flags, the banner of Gadhafi's 42 years in power, still flew above many buildings in the neighborhood, but all appeared quiet.

Medical workers at a hospital outside Sirte said four NTC fighters were killed and 43 were wounded on Wednesday.

The NTC has said it will start the process of rebuilding Libya as a democracy only after the capture of Sirte, a former fishing village transformed by Gadhafi into a showpiece for his rule, replete with lavish conference halls and hotels.

NTC Chairman Mustafa Abdel Jalil said on a visit to Sirte on Tuesday that it would take two more days to take the town.

But the remnants of Gadhafi's forces, surrounded on three sides in Sirte and with their backs to the sea, have fought tenaciously, perhaps believing they face mistreatment or worse.

Back from the front line, NTC fighters jostled as one man tried to punch a wounded prisoner and others struggled to keep him off. The prisoner repeatedly shouted that he was a civilian.

Any male of fighting age still in Sirte was under suspicion.

We were staying in a basement, one man, Gamal Ammar, said alongside family members. Some of us were hit. If we had died it would have been better. We had no water and no food. We couldn't get out. As NTC fighters drew near, he fell silent.

(Additional reporting by Tim Gaynor in Sirte, Joseph Logan and Jessica Donati; Writing by Janet Lawrence; Editing by Ron Popeski)