TRIPOLI, Libya (AP) -- 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.

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 30 miles (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.

ICC prosecutor Luis Moreno Ocampo told The Associated Press that he will travel to Libya next week for talks with the country's transitional government on where the trial will take place. Ocampo said that while national governments have the first right to try their own citizens for war crimes, he wants to make sure Seif al-Islam has a fair trial.

``The good news is that Seif al-Islam is arrested, he is alive, and now he will face justice,'' Ocampo said in an interview in The Hague. ``Where and how, we will discuss it.''

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.

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 state TV posted a photograph purportedly of Seif al-Islam in custody. He is sitting by a bed and holding up three bandaged fingers as a guard looks on, although it could not independently be confirmed where or when the picture was taken or how he was injured.

The murky circumstances surrounding the deaths of Gadhafi and another son Muatassim, and the decision to lay their bodies out for public viewing drew widespread criticism and raised questions about the commitment of Libya's new rulers to respecting human rights.

Marek Marczynski of Amnesty International urged the governing National Transitional Council 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.''

Interim Justice Minister Mohammed al-Alagi 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.

The White House said it was aware of the reports but had no immediate comment.

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.

ICC prosecutor Ocampo said jurisdiction should not be hard to determine.

``The rules are, primacy for the national authorities, depending on if they have a case,'' he said.

But he added that judges at the ICC would have to formally approve a transfer of venue, under international law.

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.''

The international community said the treatment of Seif al-Islam would be an important test for the role of rule of law in post-Gadhafi and key to reconciliation efforts, regardless of where he is tried.

``The Libyan authorities should now ensure that Seif al-Islam is brought to justice in accordance with the principles of due process and in full cooperation with the International Criminal Court,'' the European Union said in a statement.