Muammar Gaddafi's son and one-time heir apparent Saif al-Islam has been detained in the southern desert, Libya's interim justice minister and other officials have said.

Fighters from the western mountain city of Zintan announced his capture on Saturday as gunfire and car horns marked jubilation across the country at the arrest of the British-educated 39-year-old who a year ago seemed set to follow his father as Libya's leader.

Saif al-Islam and three armed companions were taken without a fight during the night, officials said. Gaddafi's son was reportedly not injured, unlike Gaddafi himself, who was killed last month after being captured by fighters in his home town of Sirte.

"We have arrested Saif al-Islam Gaddafi in [the] Ubari area," Mohammed al-Alagy, Libya's acting justice minister, said.

The younger Gaddafi is wanted for crimes against humanity by the International Criminal Court (ICC) at The Hague.