The International Criminal Court chief's prosecutor on Wednesday called for the "immediate arrest and surrender" of Moamer Kadhafi's son Seif al-Islam, who was reportedly set free by a militia in Libya.
An arrest warrant issued by the Hague-based ICC in 2011 "remains valid and Libya is obliged to immediately arrest and surrender" the late dictator's son "regardless of any purported amnesty law in Libya," Fatou Bensouda said.
Kadhafi's second son and heir-apparent was said to have been released on Friday by a militia that controls the town of Zintan in western Libya.
The group, which had held Seif al-Islam for more than five years, said he had been set free under an amnesty law promulgated by a parliament based in the country's east during the Muslim holy month of Ramadan.
But the prosecutor general's office in Tripoli, where a rival UN-backed administration is based, said the amnesty could not apply to Seif al-Islam because of the severity of his crimes, saying he was still wanted for a 2015 conviction.
There was however no independent confirmation of Seif al-Islam's release, which could spark further instability in a country already wracked by divisions and violence.
Bensouda said the world war crimes court -- where he is wanted for crimes against humanity including murder -- is now "verifying" Seif al-Islam's whereabouts.
She called on Libya, the UN Security Council and "all other relevant" countries "to provide my office with any relevant information in their possession".
The ICC also called for the arrest and surrender of Libya's former security chief Al-Tuhamy Mohamed Khaled, who is wanted on similar charges for his role in attempting to quash the 2011 revolt against slain strongman Kadhafi.
The ICC in April unveiled an arrest warrant for Khaled.
"It is imperative for both suspects to be apprehended and immediately surrendered to the custody of the ICC so that their guilt or innocence can be established," Bensouda said.
"For justice to be done, and seen to be done."
Seif al-Islam's whereabouts remain a mystery and even his lawyer, Karim Khan, has declined to confirm or deny the militia has let him go.
Seif al-Islam had been held in Zintan since being detained in November 2011, just days after his father was killed in a NATO-backed uprising against his decades-long rule.
The Zintan militia, which opposes Libya's UN-backed Government of National Accord (GNA) based in the capital, had refused to hand him over to authorities despite several legal cases.
A court in Tripoli convicted Seif al-Islam in 2015 in connection with attempts to put down the revolt and sentenced him in absentia to death.
His reported release came with the North African country still rocked by infighting, with authorities in the east, reportedly allied with the forces of military strongman Khalifa Haftar, refusing to recognise the GNA.
Born in the Janzour area of Libya, west of Tripoli, in 1942, Khaled was known by several aliases, and had "at least 10 different passports, some issued under other identities," his arrest warrant says.
According to Libyan media, Khaled was arrested in Cairo in April 2012, but was released again as there was no warrant against him. Since then he is believed to have dropped out of sight.