In this July 11, 2018 photo, US President Donald Trump, right, walks in with Secretary of Defense Jim Mattis, as they arrive to attend the multilateral meeting of the North Atlantic Council in Brussels, Belgium. (PABLO MARTINEZ MONSIVAIS / POOL / AFP)

WASHINGTON – US President Donald Trump said on Wednesday that Defense Secretary Jim Mattis will remain in office, dismissing reports that he is looking for possible replacements for the Pentagon chief.

We're very happy with him (Jim Mattis). We're having a lot of victories. 

Donald Trump, US President

"He'll stay right there. We're very happy with him. We're having a lot of victories," Trump said when asked by reporters at the White House whether he was considering replacing Mattis.

The remarks came as Washington Post columnist Josh Rogin wrote in an article released earlier Wednesday that the administration has been considering possible replacements for Mattis for weeks.

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Rogin added that no decisions have been made, though White House officials expect that Mattis will leave his position in the coming months.

The Trump-Mattis relationship was put under limelight a day earlier after excerpts from an explosive book claimed the defense secretary had made disparaging remarks about the president.

According to the book, "Fear: Trump in the White House," authored by veteran investigative reporter Bob Woodward, Mattis was quoted as having told associates that Trump acted like "a fifth- or sixth-grader."

Mattis denied Tuesday night that he ever said or heard the quotes attributed to him in the book.

"While I generally enjoy reading fiction, this is a uniquely Washington brand of literature, and his anonymous sources do not lend credibility," Mattis said in a statement.

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Trump called Woodward's book "a total piece of fiction" on Wednesday, while praising Mattis' statement as "beautiful."

In a statement to The Washington Post, Woodward said, "I stand by my reporting."

According to the author, the book was based on hundreds of hours of conversations with direct players.

Woodward has been a reporter at The Washington Post since 1971 and remains an associate editor.

He is most famous for breaking the story of the Watergate scandal, which led to the resignation of Richard Nixon from the presidency in 1974.