Defense Secretary Jim Mattis on Tuesday slammed Bob Woodward’s book about the Trump administration, which claimed he had said the president had the understanding of a “fifth or sixth grader.”

“The contemptuous words about the President attributed to me in Woodward’s book were never uttered by me or in my presence. 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.

Notably, the statement came while he was traveling to South Asia, to work on advancing the U.S.-India defense relationship. It came just hours after the Washington Post published an article on the book, which also claimed that Chief of Staff John Kelly had made derogatory remarks about the president.

Mattis continued:

While responsible policy making in the real world is inherently messy, it is also essential that we challenge every assumption to find the best option. I embrace such debate and the open competition of ideas. In just over a year, these robust discussions and deliberations have yielded significant results, including the near annihilation of the ISIS caliphate, unprecedented burden sharing by our NATO allies, the repatriation of U.S. service member remains from North Korea, and the improved readiness of our armed forces. Our defense policies have also enjoyed overwhelming bipartisan support in Congress.

Since he took office, Mattis has repeatedly batted down to reporters the notion that he is out of step with President Trump. Earlier this year, he called an NBC News story that Pentagon leadership had gone into “damage control mode” hours after Trump left the NATO summit “fiction.”

Breitbart News exclusively reported that Mattis had actually told senators that the summit was one of the “most productive” he had ever attended. He said publicly last week during a press conference that others felt the same.

Finally, he called the suggestion that he would show contempt for Trump or tolerate disrespect for the office within the Pentagon a “product of someone’s rich imagination.”

“In serving in this administration, the idea that I would show contempt for the elected Commander-in-Chief, President Trump, or tolerate disrespect to the office of the President from within our Department of Defense, is a product of someone’s rich imagination.”