The prosecutor of the International Criminal Court says he's concerned about whether Moammar Gadhafi's son Seif al-Islam, recently captured in Libya's southern desert, will get a fair trial.

Luis Moreno Ocampo said Saturday he will travel to Libya next week for talks with the country's transitional government on where Seif al-Islam Gadhafi will be tried.

"The good news is that Seif al-Islam is arrested, he is alive, and now he will face justice," Ocampo said in an interview Saturday in The Hague.

The ICC had earlier said that it was in indirect negotiations with a son of Moammar Gadhafi about his possible surrender for trial.

Libya TV aired this photo, which purports to show Seif al-Islam in custody, sitting by a bed and holding up three bandaged fingers as a guard looks on. He later told Reuters on Saturday that the injuries were suffered during a NATO air strike a month ago. Libyan TV/AP

Ocampo said while national governments have the right to try their own citizens for war crimes, he is concerned that Gadhafi will have a fair trial and that he be tried for the same charges he faces at the ICC.

Later on Saturday, the Libyan prime minister officially declared the capture of Seif al-Islam.

"We assure Libyans and the world that Seif al-Islam will receive a fair trial ... under fair legal processes which our own people had been deprived of for the last 40 years," Abdurrahim El-Keib said at a news conference in the western town of Zintan, where Saif al-Islam and several bodyguards had been taken.

Meanwhile, a U.S. State Department official said that it could not "independently confirm" reports of Seif's capture but added that Libyan authorities have been urged to treat all prisoners in their custody in line with international standards.

Seif al-Islam — the only member of the ousted ruling family to remain at large — was considered the presumed heir to the Gadhafi reign. With a PhD from the London School of Economics, he was considered the Western face of the regime.

Celebratory gunfire shook the Libyan capital as news of his capture spread.

A spokesman for the Libyan fighters who captured him said Seif al-Islam was detained about 50 kilometres west of the town of Obari with two aides as he was trying to flee to neighbouring Niger, but the country's acting justice minister later said the convoy's destination was not confirmed.

The International Criminal Court had charged Gadhafi, Seif al-Islam and Libya's former intelligence chief Abdullah al-Senoussi with crimes against humanity for the brutal crackdown on dissent as the uprising against the regime began in mid-February and escalated into a civil war.

Seif al-Islam's capture leaves only al-Senoussi at large.

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. A journalist who interviewed Seif after his capture said his wounds were suffered during a NATO airstrike in Bani Walid in the mountains in October.

Gadhafi to be sent to Tripoli

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.

International human rights groups have called for Seif al-Islam to be transferred to The Hague out of concern for his safety after Moammar Gadhafi's death at the hands of opposition forces last month.

Seif al-Islam Gadhafi, at 39 the oldest of seven children of Moammar and Safiya Gadhafi, had long drawn western favour 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.