Muammar Qaddafi's eldest son Mohammed surrendered to rebels on Sunday, the Libyan rebel transitional council coordinator said, shortly after Colonel Qaddafi’s second son Seif Al Qaddafi was captured by rebels in their advance on Tripoli.
Embattled Libya leader Col. Qaddafi made a second appeal late Sunday for his people to "save Tripoli" from a rebel offensive, in an audio message played on state television on Sunday.
He called on the people of Tripoli on Sunday to "purge the capital" after rebels seized various parts of the city in their drive to unseat him.
The people should "go out now to purge the capital," Col. Qaddafi said, adding that there was "no place for the agents of colonialism in Tripoli and Libya."
"Go back where you came from," he added, addressing the rebels.
"It is the obligation of all Libyans. It is a question of life or death," he said. Colonel Qaddafi had 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 Gaddafi posters, the first images from the city since rebels entered from the west earlier in the day.
Col. Qaddafi also said he is prepared to negotiate directly with head of the rebel National transitional council after his son Seif Al Islam was captured by rebels Sunday night during their strategic advance on Tripoli.
Government spokesman Moussa Ibrahim said on state television that Colonel Qaddafi is ready for immediate negotiations with rebels seeking to oust him, and has asked NATO to convince the rebel forces to halt an attack on Tripoli.
Mr. Ibrahim added that 1,300 people had been killed in fighting in Tripoli on Sunday.
Meanwhile, NATO called the situation in Libya "very fluid" on Sunday as rebel fighters streamed into the capital Tripoli, and said the rule of Muammar Qaddafi was "crumbling."
"It's a very fluid situation. We can see that the regime is crumbling, and the sooner Qaddafi realizes he cannot win this war against his own people, the better," NATO spokeswoman Oana Lungescu said.
"He's the one who's responsible for starting the conflict and he should spare his people further bloodshed," she added.
Earlier, Muammar Qaddafi's presidential guard had surrendered to Libya's rebels, Al Arabiya reported on Sunday, citing the rebel National Transitional Council after reports came in that the rebels captured Muammar Qaddafi's son, Seif Al-Islam during their strategic advance on Tripoli.
Rebel national transitional council head Mustafa Abdul Jalil confirmed Seif Al Islam’s capture: "We have confirmed information that our guys have captured Seif Al Islam."
"We have given instructions to treat him well so that he can face trial."
“He is being kept in a secure place under close guard until he is handed over to the judiciary," Abdel Jalil said, without giving a date or place for the reported capture of Qaddafi's son.
In an interview with Al Arabiya TV earlier on Sunday, Mr. Abdul Jalil said if rebels were to capture Seif Al Islam they would treat him in accordance to international conventions and allow to be tried freely and fairly in a civil court.
“We will be dealing with them like any other prisoners [in Libya] according to international conventions, and we will give them a fair trial, much like former Presidents who are now being tried in civil courts,” he said in reference to recently ousted former leaders in the Arab world facing trials for corruption.
Libyan rebels have been closing in on Tripoli since Saturday night in a series of explosions and gunfire battles with forces loyal to the Qaddafi regime.
The unrest in the Libyan capital provoked the embattled Libyan leader to speak out on Sunday. In an audio message broadcast on Libyan state TV, Colonel Qaddafi said he would stay in Tripoli "until the end" and called on his supporters around the country to help liberate the capital from a rebel offensive.
"The time is now to fight for your politics, your oil, your land," he said. "I am with you in Tripoli - together until the ends of the earth," Col. Qaddafi shouted.
Col. Qaddafi added that he was "afraid that Tripoli will burn" and said he would provide weapons to supporters to fight off the rebels.
Meanwhile, the United States is closely watching the events in Tripoli and urged on Sunday that the National Transitional Council (TNC) to start planning for the post-Qaddafi era in Libya.
"Clearly the offensive for Tripoli is under way," State Department spokesperson Victoria Nuland said in a statement.
"We continue efforts to encourage the TNC to maintain broad outreach across all segments of Libyan society and to plan for post-Qaddafi Libya. Qaddafi's days are numbered. If Qaddafi cared about the welfare of the Libyan people, he would step down now."