The 12-year-old grandson of former al-Qaeda chief Osama bin Laden has reportedly been killed in an airstrike along the Pakistan-Afghan border.

The 12-year-old grandson of former al-Qaeda chief Osama bin Laden has reportedly been killed in an airstrike along the Pakistan-Afghan border.

Osama bin Hamza bin Laden died earlier this year, according to a leaked letter sent by his father Hamza bin Laden to his family announcing the death.

"The grandson of the martyr, our son Osama… has ascended to the highest paradise of heaven," said the letter - dated to this year's Islamic month of Dhu al-Qidah, which fell between July and August.

"Tragedies that we meet only the way such as these only make us stronger and more steadfast," the letter added, without stating the cause of death.

Pan-Arab news website Arabi 21 reported - citing jihadi sources - that Osama was killed during an air raid attack on an al-Qaeda base along the Pakistan Afghanistan border.

Osama's father Hamza bin Laden has become active as an al-Qaeda propagandist since his father's death at the hands of US special forces in 2011 in Pakistan.

In January, the US added Hamza bin Laden to its terrorist blacklist.

Earlier this year, the CIA released a vast archive of intimate al-Qaeda documents seized in the deadly 2011 raid on his Pakistani compound.

The huge trove included the first public images of his son Hamza as an adult.

A video of Hamza Bin Laden's wedding gave the world public the first image of Bin Laden's favourite son as an adult - footage apparently shot in Iran.

Previous document releases, show that Bin Laden was grooming Hamza to succeed him as leader of al-Qaeda's global jihadist campaign.