Hamza Bin Laden, the son of al-Qaeda founder Osama Bin Laden, died in an air strike, US media outlets report, citing intelligence officials.
The place and date of death were unclear. The Pentagon did not comment.
Bin Laden, thought to be aged about 30, had released audio and video messages calling for attacks on the US and other countries.
As recently as February, the US government offered $1m (£825,000) for information leading to his capture.
His death was widely reported by US media outlets including NBC News, the New York Times and CNN, citing unnamed US intelligence officials.
Bin Laden was seen as an emerging leader of al-Qaeda. The reports say he was killed in a military operation in the last two years and the US government was involved, but the exact date and time were unclear.
President Donald Trump declined to comment when questioned by reporters on Wednesday, as did the White House national security adviser, John Bolton.
There was no confirmation from al-Qaeda. Supporters of the Islamist militant group have urged caution over the reports and are awaiting an official announcement from its leaders, according to analysts at BBC Monitoring.
Who was Hamza Bin Laden?
Hamza Bin Laden was officially designated by the US as a global terrorist two years ago. He was widely seen as a potential successor to his father.
He was believed to have been under house arrest in Iran, although other reports suggest he may have been based near the Afghan-Pakistani border.
He is thought to have been born in Jeddah in Saudi Arabia before spending years with his mother in Iran.
The US state department says Bin Laden married the daughter of Abdullah Ahmed Abdullah, or Abu Muhammad al-Masri, who was indicted for his alleged involvement in the 1998 bombings of the US embassies in Tanzania and Kenya.
In 2011, US special forces killed his father, Osama, in a compound in Abbottabad, Pakistan. He had approved the attacks on the US on 11 September 2001, in which nearly 3,000 people were killed.
The US state department says documents seized in that raid suggest Hamza Bin Laden was being groomed to take over the leadership of al-Qaeda. A video of his wedding was found among thousands of other documents.
In 2017, a leaked message from Bin Laden to his family reportedly informed them that his 12-year-old son had been killed. The circumstances of his son’s death were unclear.
In recent years, al-Qaeda released 11 audio messages from Bin Laden in which he threatened the US, called for attacks to avenge his father’s death and encouraged jihadist action in Syria.
In March 2018, in his last known public statement, he called on the people of the Arabian Peninsula to revolt. Saudi Arabia stripped him of his citizenship in March.
Al-Qaeda’s status was undermined during the past decade as the Islamic State group rose to prominence.
It is a sign of how little is known about Hamza Bin Laden that US officials were never able to definitively confirm his age.
In recent months they had floated suggestions that he might be in Afghanistan, Pakistan or Iran. But they could not even say for sure in which country one of America’s “most wanted” was hiding.
The million-dollar price tag for information was a measure not just of the potential danger he posed but also his symbolic importance to al-Qaeda and its propaganda machine.
Bin Laden was only a child when his father helped plot the 9/11 attacks but, according to the extremist group’s legend, he was by his side at the time.
For a son brought up to hate America, avenging his killing at the hands of special forces was always going to be an obsession. In recent years he sent online messages calling for attacks against the US and its allies.
Bin Laden’s death, if officially confirmed, will silence someone who was emerging as a new voice of Al-Qaeda. However it will not end the threat from an organisation that carried out the world’s most notorious terror attack.
Emerged in Afghanistan in the late 1980s, as Arab volunteers joined US-backed Afghan mujahideen fighting to expel the occupying Soviet forces
Osama Bin Laden set up an organisation to help the volunteers, which became known as al-Qaeda, or “the base”
He left Afghanistan in 1989, returning in 1996 to run military training camps for thousands of foreign Muslims
Al-Qaeda declared “holy war” on Americans, Jews and their allies