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!"
Officials quoted anonymously by various media outlets said US forces targeted the militant leader in a raid in northwest Syria.
A US official told Reuters news agency an operation took place but was unable to confirm speculation that Baghdadi was killed.
The IS leader has been wrongly reported to be dead on previous occasions.
The White House has not confirmed either that an operation took place, or its alleged outcome.
The raid was carried out by special operations forces after they received "actionable intelligence", Newsweek said, citing unnamed sources.
Following the reports, UK-based war monitor the Syrian Observatory for Human Rights said helicopter gunfire had killed nine people near a village in Syria's Idlib province, where "groups linked to the Islamic State group" were present.
Mr Trump is set to make his statement at 09:00 (13:00 GMT) on Sunday.
Who is Abu Bakr al-Baghdadi?
The IS leader has been described as the world's most wanted man.
In October 2011, the US officially designated him a "terrorist" and offered a $10m (£5.8m; 7.3m euros) reward for information leading to his capture or death.
Baghdadi has a reputation as a highly organised and ruthless battlefield tactician.
He was born near Samarra, north of Baghdad, in 1971, and his real name is Ibrahim Awad al-Badri.
Reports suggest he was a cleric in a mosque in the city around the time of the US-led invasion in 2003.