Slain leader Muammar Gaddafi's son Seif al-Islam, wanted by the ICC for crimes against humanity, appeared for the first time in a Libyan court on Thursday on charges of "undermining state security," a judicial official said.

He was charged after a controversial June visit to Libya of an International Criminal Court team to help him prepare his defence against the charges of crimes against humanity in the conflict that overthrew his father.

Thursday's trial was held behind closed doors in Zintan, a hilltop town southwest of Tripoli, where Seif has been in custody since his arrest in November 2011 in the wake of the uprising that ended Gaddafi's 40-year rule.

"The first hearing in the trial of Seif al-Islam Gaddafi on charges of undermining state security was held on Thursday," said deputy prosecutor general Taha Baraa in Tripoli.

The accusation was levelled against Seif after four ICC envoys travelled to Zintan in June and were detained for nearly a month, triggering a diplomatic row with The Hague-based court. They were finally allowed to return home in July.

The four included Australian lawyer Melinda Taylor who was accused of carrying a pen camera and attempting to give Seif a coded letter from his former right-hand man, Mohammed Ismail, who is wanted by Libyan authorities.

The other ICC staffers were Taylor's interpreter from Lebanon, Helen Assaf, and two colleagues, Russian Alexander Khodakov and Spaniard Esteban Peralta Losilla.

All four have also been accused by Libya of undermining its national security.

Baraa said the trial was adjourned to May 2 as time was needed to inform the ICC staffers of the charges against them, and to "designate a lawyer for Seif."

Thursday's hearing came as the ICC mulls a Libyan request to allow Seif, and former Libyan spy chief Abdullah Senussi, to be tried at home instead of in The Hague.

The ICC, which was mandated by the UN Security Council to investigate the Libyan conflict, issued arrest warrants in June 2011 for both Seif and Senussi on charges of crimes against humanity.

Lawyers for Seif and Senussi have said they will not get a fair trial in Libya.