WASHINGTON/BEIRUT • The US has offered a US$1 million (S$1.35 million) reward for information on a son of the late Al-Qaeda leader Osama bin Laden, seeing him as an emerging face of extremism.

Separately, in a statement published by the official gazette Umm Al Qura yesterday, Saudi Arabia's Interior Ministry said it has stripped Hamza bin Laden of his citizenship.

The location of Hamza, sometimes dubbed the "crown prince of jihad", has been the subject of speculation for years, with reports of him living in Pakistan, Afghanistan, Syria or under house arrest in Iran.

"Hamza bin Laden is the son of deceased former AQ leader Osama bin Laden and is emerging as a leader in the AQ franchise," a US State Department statement said, referring to Al-Qaeda.

Hamza, who according to the United States is aged around 30, has threatened attacks against the US to avenge the 2011 killing of his father, who was living in hiding in the Pakistani garrison town of Abbottabad, by US special forces.

US intelligence agencies increasingly see the younger bin Laden as a successor to his father for the mantle of global terrorism especially as the even more extreme Islamic State in Iraq and Syria is down to its last sliver of land in Syria.

In 2015, Hamza released an audio message urging extremists in Syria to unite, claiming that the fight in the war-torn country paves the way to "liberating Palestine".

In a message a year later, following in the footsteps of his father, he urged the overthrow of the leadership in their native Saudi Arabia.

Osama's three surviving wives, and his children were quietly allowed to return to Saudi Arabia after his killing.

It is believed that he spent years, along with his mother, in Iran, despite Al-Qaeda's strident denunciations of the Shi'ite branch of Islam that dominates the country.

Observers say the clerical regime in Teheran had kept him under house arrest as a way to maintain pressure on its rival Saudi Arabia as well as on Al-Qaeda, dissuading the Sunni militants from attacking Iran.

One of Hamza's half-brothers told British newspaper The Guardian last year that Hamza's whereabouts were unknown but that he may be in Afghanistan.

He also said that Hamza had married the daughter of Mohammed Atta, the lead hijacker in Al-Qaeda's Sept 11, 2001, attacks on the US that killed some 3,000 people and sparked the US intervention in Afghanistan.

AGENCE FRANCE-PRESSE, REUTERS