The International Criminal Court is demanding the immediate release of four of its members detained in the Libyan town of Zintan since Thursday.
Australian lawyer Melinda Taylor and three others are accused by local militia of carrying spying material and suspicious documents.
They had been trying to see Saif al-Islam, Muammar Gaddafi’s son who is being held on crimes relating to last year’s war.
Ahmed al-Jehani, the Libyan lawyer in charge of Saif’s case and liaison between Tripoli and the ICC said the delegation’s bags had undergone a routine search and were found to contain documents and letters for Saif along with a pen with a camera and a watch with recording material.
He said the team was being held in a guesthouse for questioning.
The ICC wants to try Saif al-Islam at the Hague but Tripoli wants him tried at home. The delegation travelled to Zintan on Wednesday to meet him and discuss his defence.