Four members of the International Criminal Court were detained in the Libyan town of Zintan last week. The ICC team was there trying to meet with Saif al-Islam Gadhafi.
ICC President Song Sang-hyun said the court, based in The Hague, Netherlands, was concerned about the welfare of the staff members. He said the court was in contact with authorities in Libya to secure their release but hasn't had contact with the missing members.
"These four international civil servants have immunity when on an official ICC mission," Song said in a statement. "I call on the Libyan authorities to immediately take all necessary measures to ensure their safety and security and to liberate them."
The ICC in June 2011 issued arrest warrants for Saif al-Islam and former Libyan intelligence chief Abdullah al-Senussi for alleged crimes against humanity, notably murder and persecution, committed allegedly in Libya during the early stages of last year's civil war.
The interim administration in Tripoli submitted a challenge to the ICC claiming Saif al-Islam and Senussi should be tried before national courts.