The International Criminal Court in the Hague says four of its staffers have been detained in Libya, where they are part of an official mission to meet with Saif al-Islam Gadhafi, the imprisoned son of deposed dictator Moammar Gadhafi.

Court President Sang-Hyun Song requested their immediate release and urged Tripoli to ensure their safety. His statement issued Saturday said “these four international civil servants have immunity when on an official ICC mission.”

The four, including Australian lawyer Melinda Taylor, were detained Thursday as they were trying to meet with Saif al-Islam Gadhafi in Zintan, southwest of Tripoli, where he has been held by revolutionary fighters since his capture in November. The delegation has been assigned by the court to discuss his defense arrangements.

Sources in Libya say Taylor was trying to pass documents to Saif during the visit. They said police also found a camera and a recording device on another female member of the delegation during a search after the visit.

Libya's representative to the ICC, Ahmed al-Jahani, said Taylor was “not in prison but under house arrest in Zintan” where she was being questioned.

Saif al-Islam is at the center of a wrangle between the ICC and the new government in Tripoli. He is wanted by the ICC for alleged war crimes, but Tripoli wants to try him in his home country.