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 death, 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 earlier Saturday in Libya that authorities in Zintan, southwest of Tripoli, had detained Australian defense lawyer Melinda Taylor.
He said that authorities took her camera and recording device before her Thursday meeting with Seif al-Islam, but that inside she shared documents that they said could harm Libya's national security, including information and drawings that could endanger Libyans living abroad.
The ICC statement noted that it had been empowered by the United Nations Security Council to deal with Seif al-Islam's case, and that Libya is obliged to obey court rules that ensure "rights of the suspects to have privileged contacts with their lawyers."
Jehani said that Taylor is being held in a guesthouse in Zintan where her colleagues are staying. He said she would likely be released soon.