Libya holds four ICC staff after they met Saif Gaddafi
Libyan authorities have detained four members of the International Criminal Court's staff who had gone to meet Saif al-Islam, son of former Libyan leader Colonel Gaddafi, the ICC says.
ICC president Sang-Hyun Song urged Libya to immediately "liberate them".
He said the civil servants had been held since Thursday 7 June.
Earlier reports said an ICC lawyer was being held under house arrest accused of trying to pass what were said to be dangerous documents to Saif al-Islam.
The delegation travelled to Libya on 6 June, to meet Saif Al-Islam Gaddafi in Zintan, "in part as a privileged visit by the Office of Public Counsel for the Defence, currently appointed to represent Mr Gaddafi in the case brought against him," the ICC president said in a statement.
"We are very concerned about the safety of our staff in the absence of any contact with them," the statement said.
"These four international civil servants have immunity when on an official ICC mission. I call on the Libyan authorities to immediately take all necessary measures to ensure their safety and security and to liberate them."'Documents discovered'
Saif al-Islam, who was captured last November by militiamen as he tried to flee the country, has been indicted by the ICC for crimes against humanity.
Libya's interim government has so far refused to hand over Saif al-Islam for trial in the Netherlands - seat of the ICC. Libya has insisted he should be tried by a Libyan court.
Members of the brigade holding Saif al-Islam say they discovered documents including a letter from a former confidante of his who is now in Egypt, the BBC's Rana Jawad reports from Zintan.
The brigade commander said the transitional authorities in Tripoli had requested the release of the ICC officials, but they would remain in detention in Zintan - "where the crime has been committed" - pending an investigation by the attorney general's office.
Reporters were shown the documents from a short distance, but were not allowed to view them in person, our correspondent says.
Those detained are reported to include an Australian lawyer, identified as Melinda Taylor.