Photo: Saadi Gaddafi in 2005 at a news conference in Sydney, where he was travelling with the Libyan football team
Libya had been seeking the extradition of Saadi, who had fled to the southern neighbour nation after his father Gaddafi was toppled in a Nato-backed uprising in 2011.
Pictures that appeared to show Saadi with a shaved head and beard, and wearing a blue prison uniform, were posted online on Thursday morning.
Saadi, the third of Muammer Gaddafi’s seven sons, is now being held by judiciary police forces, the government said. It thanked Niger for its cooperation and said Saadi would be treated according to international justice standards for prisoners.
The website of a government-backed militia showed what it said were pictures of Saadi wearing a blue prison uniform, calling him a criminal. Libyan news websites also ran pictures showing him with his head shaven in prison.
On its official Facebook page, a statement from the Libyan government said: “The Libyan government thanks the president of the Republic of Niger, Mahamadou Issoufou, we also thank the Niger government and the people of Niger for their cooperation with the Libyan government in pledging its commitment to the treatment of the accused on the principles of justice and international norms in dealing with prisoners.
“God save Libya.”
The ICC has indicted Saif al-Islam for crimes against humanity. Saif, once viewed as a likely successor to his father, is held by a militia in western Libya, where he is being tried for various charges.