The International Criminal Court prosecutor said on Sunday Saif al-Islam, the son of Libya's Muammar Gaddafi, had been detained in Libya.

"Saif was captured in Libya," prosecutor Luis Moreno-Ocampo told Reuters. "We have confidential information from different sources that we have within Libya confirming this." Libyan state TV is broadcasting recorded programmes, says its transmission jammed.

Gaddafi made two audio addresses over state television calling on Libyans to fight off the rebels.

"I am afraid if we don't act, they will burn Tripoli," he said. "There will be no more water, food, electricity or freedom."

Libyan rebels waved opposition flags and shot into the air in jubilation after reaching Tripoli's central Green Square, Sky news live footage from the scene showed in the early hours of Monday.

The vast square, reserved until now for carefully orchestrated rallies praising Muammar Gadhafi, erupted in celebration after rebel troops pushed into the centre of the Libyan capital overnight.

Libyan rebel forces seized the Green Square in downtown Tripoli on Sunday night, Al-Jazeera TV Channel reported.

Libyan leader Muammar Gaddafi's rule in Libya is "clearly crumbling," NATO Secretary General Anders Fogh Rasmussen said early Monday, shortly after Libyan rebels launched attacks on Tripoli on late Sunday.

1,300 people killed in fighting

BENGHAZI/TRIPOLI - The spokesman for Libyan leader Muammar Gadhaf's government Moussa Ibrahim said on Sunday that 1,300 people had been killed in the fighting in Tripoli since noon Sunday.

Libyan leader Muammar Gadhaf's most prominent son, Saif al-Islam, speaks during an interview with Reuters in Tripoli in March 10, 2011 file photograph. [Photo/Agencies]

He said at a press conference in Tripoli that 5,000 people were wounded in the battle and the NATO should be held responsible for the bloodshed.

He said that the country needs Gadhaf and people should be encouraged to fight for him.

Mustafa Abdul Jalil, the head of Libya's National Transitional Council (NTC), said in an TV interview earlier Sunday night that Saif al-Islam, Gadhaf's second son, had been captured and was under custody in a safe place.

Jalil said that Gadhaf's guards in Tripoli had surrendered to the opposition troops.

Opposition convoy entered the western district of Tripoli on Sunday with almost no sign of resistance, Al-Jazeera TV channel reported.  

Residents of the city began to stream into streets to welcome the opposition troops, despite Gadhaf's call to urge people to take up arms to guard his rule.

The opposition troops were only about 8 km west to the city center, Al-Jazeera reported.

People in Benghazi, the rebels' stronghold, celebrated when they heard the news of Saif's capture, by shooting gunfire into the sky. The cars on the street were horning along the gunfire.

Gadhafi made a second appeal for his people to "save Tripoli" from a rebel offensive, in an audio message played on state television on Sunday.

"It is the obligation of all Libyans. It is a question of life or death," he said. Gaddafi made a similar appeal earlier in the evening on state television, as rebels streamed into the capital.

Al Arabiya television aired images of Libyans celebrating in central Tripoli and tearing down Gadhafi posters, the first images from the city since rebels entered from the west earlier in the day.