Libya has put four International Criminal Court (ICC) envoys in "preventive" detention in prison for 45 days while investigating an alleged threat to national security, a judicial source said on Monday.
"A decision was made to put them in preventive detention for 45 days while investigations are conducted," an official in the attorney general's office told AFP on condition of anonymity.
Ajmi al-Atiri, head of the brigade in Zintan that detained the delegation after it visited Moamer Kadhafi's son Seif al-Islam, said: "They were transferred yesterday (Sunday) to a prison on the orders of the prosecutor general."
The four-member delegation has been held since Thursday in the western town after one of its lawyers, Melinda Taylor, was found carrying documents for Seif al-Islam that were considered a "threat to national security."
Taylor works with Xavier-Jean Keita, the defence counsel that the ICC appointed for Seif al-Islam.
The team was in Libya to help Seif choose a defence lawyer, and the court has said the visit was authorised by the country's chief prosecutors.
Ahmed Jehani, Libya's envoy to the ICC, has said that the Australian lawyer was caught "exchanging papers with the accused Seif al-Islam."
Jehani alleged that Taylor was carrying a pen camera and a letter from Mohammed Ismail, Seif's former right-hand man who is now on the run.
He said the letter contained drawings and symbols, a "code" that would be understood only by the sender and the intended recipient, Seif.
"According to Libyan law, it would be spying, communication with the enemy," the envoy said.
Jehani said that Taylor's interpreter Helene Assaf, a Lebanese who has been working with the ICC since 2005, was considered an "accomplice."
The ICC has named the other members on the team as Russian Alexander Khodakov and Esteban Peralta Losilla from Spain.
According to Jehani, the two men had stayed behind out of their own accord.
Atiri gave no explanation as to why the men had been transferred from a house, where the team was initially held, to a formal detention facility.
Keita called on Monday for the immediate release of his colleagues.
"As a counsel and as a court official, I call for the immediate release of my four colleagues who are being illegally detained in Libya," the head of the ICC's public defence office told AFP.
He said the conditions under which Taylor and Assaf were to meet Seif had been established by judges and accepted by the Libyans.
There were to be "no witnesses, no recordings, no video and the ability to speak freely," Keita said, adding that a visit two months ago went ahead without any problem.
Meanwhile, the interim government spokesman said he hoped that the ICC will cooperate with Libyan authorities in a "neutral investigation."
"Relations between Libya and the ICC cannot be at the expense of Libya's highest national interest," the state news agency LANA quoted Nasser al-Manaa as saying.
"We expect the ICC to understand Libya's position and cooperate in a neutral investigation," he said, adding that further measures will be determined depending on the findings of the investigation.
The ICC wants to try Seif, 39, for crimes against humanity in The Hague while the new regime regime in Libya insists he should face justice at home.
Ex-rebels in Zintan who have held Kadhafi's son since his arrest on November 19 last year refuse to send him to Tripoli for fear that he might escape.
A new ICC team arrived in Libya on Sunday to negotiate with the authorities, and on Monday met officials including attorney general Abdelaziz al-Hasadi, his office said.
Keita said they had not been able to make contact with the detainees.