Ousted Libyan leader Muammar Gaddafi's son Seif al-Islam will go on trial in September in the Libyan town of Zintan where he has been held since last November, the prosecution's spokesman told media outlets on Thursday.

"A committee from the prosecutor general's office has completed its investigation into the crimes committed by Seif al-Islam from the start of the revolution on February 15 (2011) and has prepared the chargesheet," spokesman Taha Nasser Baara said.

He said the chargesheet would be "approved by the prosecutor general in the coming days and a date set for the September trial opening" in Zintan, a hilltop town 170 kilometers southwest of the Libyan capital.

The International Criminal Court in The Hague had issued a warrant for Seif's arrest on charges of crimes against humanity during the conflict which overthrew his father last year but the new Libyan authorities have insisted that he stand trial in his home country.

Activists have raised concerns that Seif, 40, could face the death penalty if tried in Libya. And Seif, his lawyers said on July 31, is pleading to be put on trial before The Hague-based court for justice to be served.