Libyan prosecutors say they are investigating the killing of Saif al-Islam Gaddafi, son of the country's long-time leader Col Muammar Gaddafi.

The 53-year-old, who was once widely seen as his father's heir apparent, was killed during a "direct confrontation" with four unknown gunmen who broke into his home in the city of Zintan, his office said in a statement.

"The victim died from wounds by gunfire," Libyan prosecutors said on Wednesday, adding that efforts were under way to identify the gunmen.

In a different version of events, his sister told Libyan TV that he had died near the country's border with Algeria.

Saif al-Islam's lawyer told the AFP news agency a "four-man commando" unit carried out an assassination at his home in the city of Zintan, though it was not clear who may have been behind the attack.

The public prosecutor's office said forensic experts had been dispatched to Zintan in north-west Libya to conduct investigations.

Saif al-Islam was long seen as the most influential and feared figure in the country after his father, who ruled Libya from 1969 until being ousted and killed during an uprising in 2011.

BBC World Affairs editor John Simpson, who had met Saif al-Islam Gaddafi, said that he was "a strange, mercurial figure, but he was much less eccentric than his father".

"During the 2011 revolution, he agreed to be interviewed for the BBC, only to scream insults at me in front of his officials," Simpson said.

"Then he sent them away, and apologised profusely. 'They expect it of me,' he said."

According to Libyan journalist and writer Abdulkader Assad, Saif al-Islam might have been targeted by locals who felt their political influence was being threatened by his popularity.

"It could also be foreign actors took him out because of his controversial past," Abdulkader told the BBC's Newsday programme.

Born in 1972, he played a key role in Libya's rapprochement with the West from 2000 until the collapse of the Gaddafi regime.

After his father's removal, Saif al-Islam Gaddafi - who was accused of playing a key role in the brutal repression of anti-government protests - was jailed by a rival militia in the city of Zintan for almost six years.

The International Criminal Court (ICC) wanted to put him on trial for crimes against humanity for his alleged role in the suppression of opposition protests in 2011.

In 2015, he was given a death sentence in absentia for his role in the crackdown by a court in Tripoli, in the west of the country, where control is in the hands of the UN-backed government.

But he was released by militia in Tobruk, in the east, under an amnesty law two years later.

Simpson attended his trial in Zintan.

"In the courtroom he greeted me and my television crew with relief, maybe thinking that our presence would save him from execution," he said.

"But he had great faith in his negotiating skills and his personal charm, and he managed to win over his captors, who eventually freed him.

"But the loathing many Libyans felt for his father extended to him, and may have brought about his death."

Since the overthrow of Gaddafi, Libya has been split into areas controlled by various militias and is currently divided between two rival governments.

During his father's time as leader, he shaped policy and led high-profile negotiations despite having no official role in government, including those which led his father to abandon his nuclear weapons programme.

Such agreements saw international sanctions on the north African country lifted, and some considered Gaddafi a reformist and acceptable face of a changing Libya.

Gaddafi had always denied that he wanted to inherit power from his father, saying the reins of power were "not a farm to inherit".

However, in 2021 he announced he would run for the presidency in elections which were then postponed indefinitely.