President Donald Trump will make a "major statement" to the nation at 9 a.m. ET Sunday, the White House said late Saturday night.

It wasn't immediately clear what Trump would discuss in his speech. The president tweeted earlier Saturday night that "Something very big has just happened!" but did not follow up with further details.

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"The President of the United States will be making a major statement tomorrow morning at 9 o'clock from the White House," White House spokesman Hogan Gidley said in a statement that came more than an hour after Trump's tweet. The White House initially said Judd Deere, another spokesman, had made the statement.

Various media outlets, including NBC News, reported that U.S. forces had carried out an operation in Syria that targeted Abu Bakr al-Baghdadi, leader of the terrorist group ISIS. Officials believed Baghdadi was killed in the operation, although, as of early Sunday morning, there had yet to be confirmation.