AMSTERDAM – 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.”

The four detained include at least one of two lawyers the court has assigned to help defend the legal interests of Seif al-Islam Gadhafi, who has been held by revolutionary fighters since his capture in November.

Seif al-Islam is at the center of a wrangle between the international court and the new government in Tripoli, both of which have drawn up plans to prosecute him for alleged war crimes.

Under international law, a country has the first right to try suspects for crimes committed on its own soil. But the ICC indicted Seif al-Islam before the fall of his father’s regime and cannot drop his case until it is convinced that Libya’s new government will prosecute him for the same crimes — and that it is capable of giving him a fair trial.

Since Gadhafi’s ouster, the new government in Tripoli has struggled to impose its authority throughout the country. Cities, towns, regions, militias and tribes all act on their own, setting up independent power centers.

The lawyer who represents Libyan interests at the Hague court, Ahmed Al-Jehani, said Saturday in Libya that authorities in Zintan, southwest of Tripoli, had detained Australian defense lawyer Melinda Taylor.