The US military has conducted an operation against the fugitive leader of the Islamic State (IS) group, US media report.
Claims of a raid against Abu Bakr al-Baghdadi have not been confirmed.
The White House said US President Donald Trump would make a “major statement” on Sunday, but gave no further details.
Mr Trump earlier shared a cryptic tweet saying: “Something very big has just happened!”
The IS leader has been wrongly reported dead on several previous occasions.
Officials quoted anonymously by various media outlets said US forces targeted the militant leader in a raid in Idlib province, in north-west Syria.
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The commander of the Kurdish-led Syrian Democratic Forces (SDF), Mazloum Abdi, said on Sunday that a “historic, successful operation” had resulted from “joint intelligence work” with the US.
A US official told Reuters news agency an operation took place but was unable to confirm speculation that Baghdadi was killed.
The White House has neither confirmed that an operation took place, nor its alleged outcome.
The raid was carried out by special operations forces after they received “actionable intelligence”, Newsweek said, citing unnamed sources.
The Syrian Observatory for Human Rights, a UK-based monitoring group, said helicopter gunfire had killed nine people near a village in the Syrian province of Idlib, where “groups linked to the Islamic State group” were present.
The BBC understands that Mr Trump is set to make his statement at 13:00 GMT (09:00 local time) on Sunday.