Islamic State leader Abu Bakr al Baghdadi is believed to have been killed after a US operation in Syria.
Al Baghdadi, who had a $25m bounty on his head, has been the subject of an international manhunt for years but there is no official confirmation as to whether the operation was successful.
Newsweek said it had been told by a US Army official that al Baghdadi was dead, as a result of the operation in Syria's northwestern Idlib province.
An official told the Associated Press that confirmation of the IS boss's death in an explosion is pending.
The Pentagon has not commented.
US President Donald Trump tweeted on Saturday night: "Something very big has just happened!" - but he gave no further explanation.