Moammar Gadhafi's son Seif al-Islam — the only wanted member of the ousted ruling family to remain at large — was captured as he traveled with aides in a convoy in Libya's southern desert, Libyan officials said Saturday.

Thunderous celebratory gunfire shook the Libyan capital as the news spread, AP news agency reported.

A spokesman for the Libyan fighters who captured him said Seif al-Islam, who has been charged by the International Criminal Court for crimes against humanity, was detained about 50 kilometers west of the town of Obari with two aides as he was trying to flee to neighboring Niger. But the country's acting justice minister later said the convoy's destination was not confirmed.

His capture just over a month after his father was killed leaves only former intelligence chief Abdullah al-Senoussi wanted by the ICC, which indicted the three men for in June for unleashing a campaign of murder and torture to suppress the uprising against the Gadhafi regime that broke out in mid-February.

"This is the day of victory, this is the day of liberation, finally the son of the tyrant has been captured," said Mohammed Ali, an engineer, as he celebrated on Tripoli's Martyrs' Square. "Now we are free, now we are free, God is Great."

Libyan TV posted a photo purportedly of Seif al-Islam in custody. He is sitting by a bed and holding up three bandaged fingers as a guard looks on. International rights groups urged the Libyans to respect his human rights.

"Seif must face justice. Whether it's in Libya or in The Hague, he should face justice. We have to coordinate together with the Libyan authorities," ICC Prosecutor Luis Moreno Ocampo said in a telephone interview.

The murky circumstances surrounding the deaths of Gadhafi and another son Muatassim, and the decision to lay their bodies out for public viewing has drawn criticism from rights groups.

Marek Marczynski of Amnesty International urged the Libyans to transfer Seif al-Islam to the ICC base in the Netherlands as soon as possible.

"The ICC has an arrest warrant out for him and that is the correct thing to do. He must be brought before a judge as soon as possible," he said. "It matters for the victims. What they need to see is true justice. They need to know the truth about what happened."

Mohammed al-Alagi, the National Transitional Council's justice minister, told The Associated Press that Seif al-Islam was detained deep in Libya's desert Friday night by revolutionary forces from the mountain town of Zintan who had been tracking him for days.

Seif al-Islam was being held in Zintan but would be transported to Tripoli soon, according to al-Alagi.

A spokesman for the Zintan brigades, Bashir al-Tlayeb, who first announced the capture at a press conference in Tripoli, said the NTC, which took over governing the country after Gadhafi was ousted, would decide where Seif al-Islam would be tried.

"Seif al-Islam was caught with two aides who were trying to smuggle him into Niger," al-Tlayeb said, adding that he had no information about al-Senoussi's whereabouts.

The justice minister, however, said Seif al-Islam was captured closer to the Algerian border and the convoy's destination was not known.

Seif al-Islam Gadhafi, at 39 the oldest of seven children of Moammar and Safiya Gadhafi, had long drawn Western favor in by touting himself as a liberalizing reformer in the autocratic regime but then staunchly backed his father in his brutal crackdown on rebels in the regime's final days.

He had gone underground after Tripoli fell to revolutionary forces and issued audio recordings to try to rally support for his father.

The International Criminal Court had earlier said that it was in indirect negotiations with a son of the late Libyan leader Moammar Gadhafi about his possible surrender for trial.

An ICC spokesman said the court was waiting for proof that Seif al-Islam had been captured but stressed Libya has a legal obligation to cooperate with the international arrest warrant.

"First we have to verify if it really is him and that he's actually been arrested this time," the spokesman, Fadi El Abdallah, said. "If they decide they want to try the suspect in Libya instead of at the ICC, there's a necessary process."

He said the Libyans could formally request that the case be transferred, then ICC judges would make a decision.

"The main criteria is that he generally be prosecuted for the same crimes," the spokesman said. "For us there's an obligation, a legal obligation under international law, for the national government to cooperate with the ICC."

Libya's Information Minister Mahmoud Shammam said the NTC had not taken an official position yet, but in his personal view, Seif al-Islam "is an outlaw and should be tried in front of the Libyan Court, by Libyan people and by Libyan justice."