AMSTERDAM (AP) — The International Criminal Court on Saturday demanded the release of four of its staffers it says are being detained in Libya, where they are part of an official mission sent to meet with the imprisoned son of deposed dictator Moammar Gadhafi.

“We are very concerned about the safety of our staff in the absence of any contact with them,” said court President Sang-Hyun Song in a statement issued in The Hague, Netherlands. “These four international civil servants have immunity when on an official ICC mission.”