Libya's Saif al-Islam Gaddafi went from his notorious father's heir apparent to a decade of captivity and obscurity in a remote hill town before launching a presidential bid that helped derail an attempted election.

Saif al-Islam's office said in a statement on Tuesday that he had been killed during a "direct confrontation" with four unknown gunmen who broke into his home. Further details were not made public.

Despite holding no official position, Saif al-Islam was once seen as the most powerful figure in the oil-rich North African country after his father Muammar Gaddafi, who ruled for more than four decades.

Determined to rid Libya of its pariah status, he engaged with the West and championed himself as a reformer, calling for a constitution and respect for human rights.

But when a rebellion broke out against Gaddafi's long rule in 2011, Saif al-Islam immediately chose family and clan loyalties over his many friendships to become an architect of a brutal crackdown on rebels, whom he called rats.