Seif al-Islam will face justice whether he is tried in The Hague or in Libya, International Criminal Court prosecutor Luis Moreno-Ocampo said on Wednesday, insisting the decision lies with the ICC.
Libyan officials, however, remain adamant that he be tried in his country.
"Judges of the ICC will decide who makes the trial," Ocampo told AFP at the start of a three-day visit to the North African nation.
"The interesting thing is that the ICC wants to do justice on Seif (and) Libya wants to do justice on Seif, (so) there will be justice for Seif," he added.
The fate of slain dictator Moamer Kadhafi's son Seif al-Islam, who is wanted by the ICC for crimes against humanity, was at the heart of his talks with senior officials in Tripoli.
The new authorities stress that they want to try Seif, 39, in his home country and are expected to challenge the ICC's jurisdiction over the case.
"Libya says they will present the challenge in the end of April, so I need to be prepared," Ocampo said ahead of a meeting with interim leader Mustafa Abdel Jalil.
"I came to check what they are doing here," he added.
The ICC issued an arrest warrant for Seif in February 2011, when pro-Kadhafi forces sought to crush a popular uprising with brutal force.
On April 10, Tripoli appealed an ICC ruling calling for Seif's immediate transfer from Libyan custody to prison in The Hague.
The interim government keeps insisting that Libyan judges are capable of giving Seif a fair trial -- a claim rights groups have called into question, noting he could face the death penalty.
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Its spokesman hammered that point again on Wednesday.
"Seif al-Islam will not be handed to the ICC because Libya considers it has a right to try him," Nasser al-Manaa told journalists.
Libya's rulers have so far failed to pry Seif out of the hands of a militia holding him in the town of Zintan, southwest of the capital.
The ICC envoy said he would not be visiting Seif because Kadhafi's son remains without a lawyer.
"I cannot see Seif because there has to be a lawyer (present) and he has no lawyer," he said, adding that one will be appointed by Libya's prosecutor.
ICC defence official Xavier-Jean Keita has alleged that Seif had been assaulted since his arrest on November 19 last year in southwestern Libya.
On Wednesday, Keita urged Ocampo "to refrain from making any public pronouncements, which impact on the appearance of the independence and impartiality of the prosecution"
Ocampo said he also plans to visit the coastal city of Misrata, the country's third largest and one of the worst hit by the war, where he is investigating rape cases.
"We believe we can present a new case there against all the individuals," he said, without specifying whether he meant former rebels or Kadhafi's fighters.
Both camps have been accused of committing war crimes in the 2011 conflict.
Human Rights Watch on April 8 warned leaders in Misrata that they could be held legally accountable by the ICC for crimes committed by militias under their command.