Niger has extradited Muammar Gaddafi's son Saadi, who has arrived in Tripoli and has been brought to a prison, the Libyan government said this morning.

The North African country had been seeking the extradition of Saadi Gaddafi, who had fled to the neighbouring nation after the toppling of his father in a NATO-backed uprising in 2011.

"The Libyan government received today Saadi Gaddafi and he arrived in Tripoli," the cabinet of Prime Minister Ali Zeidan said in a statement.

Saadi, one of Gaddafi's seven sons, is being held by judiciary police forces, the government said.

It thanked Niger for its co-operation 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.

Saadi, who had a career as a businessman and professional footballer, is not wanted by the International Criminal Court, as is Gaddafi's most prominent son Saif al-Islam.

But Libya wants to try him for allegedly misappropriating property by force and for alleged armed intimidation when he headed the Libyan Football Federation.

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.

Fighters from the western Zintan region caught Saif in the southern desert a month after his father was captured and battered to death by a mob in 2011.

The militia has defied an order from the government to deliver him to a jail in the capital.