President Donald Trump has told reporters that his Chief of Staff John Kelly will be leaving his job by the end of the year.
For several days there have been persistent reports that Mr. Kelly has been pressured.
Some reports say that the relationship between the retired Marine Corps General and Mr. Trump has deteriorated and that they no longer speak with each other.
A replacement would be called "in the next one or two days," Trump added.
He announced the announcement as he went to Philadelphia for an American football match between army and naval teams.
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Kelly's expected departure means that Trump will have three chiefs of staff and three national security advisors since taking office in January 2017, says BBC North American correspondent Anthony Zurcher.
Last month, Reuters quoted a source as saying that Nick Ayers, chief of staff of Vice President Mike Pence, was a potential contender for the role.
Earlier this year, Mr. Kelly had to deny that he had called Trump an "idiot" after the quote was added to a book by Mr. Trump by experienced investigative journalist Bob Woodward.
Mr. Kelly is said to have used the description repeatedly and allegedly said it was useless to convince him of anything.
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