The White House has warned former national security adviser John Bolton not to publish his book containing evidence about President Donald Trump’s attempts to pressure Ukraine to investigate his political rival.

National Security Council officials sent a letter to Bolton’s lawyer, saying the unpublished book appears to contain significant amounts of classified information and couldn’t be published as written.

The top secret information reasonably could be expected to cause exceptionally grave harm to the national security, the letter read.

Bolton has reportedly written in his book, The Room Where It Happened: A White House Memoir, that Trump demanded Ukraine investigate political rival, former Vice President Joe Biden, in exchange for millions of dollars in military assistance to the European nation, The New York Times reported Sunday.

Under the commencement Bolton made when he accepted the job as Trump’s national security adviser, the manuscript may not be published or otherwise disclosed without the deletion of this classified information, according to the letter.

The manuscript was sent to the Nationals Security Council (NSC) a month ago for a standard review.

The Trump administration officials said the president and his legal team have not seen the manuscript and did not participate in the review.

Bolton’s attorney Charles Cooper disputed the claim about top secret information, saying that any of that information could reasonable be considered classified.

The NSC, however, said it would work with Bolton on revisions to the book.

The dispute between the White House and Bolton comes as the news of the book prompted demands for Bolton’s testimony in the Senate impeachment trial.

Bolton said he would be willing to testify in the Senate trial if subpoenaed.

Trump, however, has threatened to assert executive privilege and block Bolton’s testimony, if necessary.

In a Twitter message on Wednesday, Trump attacked Bolton’s reputation as a military hawk, describing the book as nasty and untrue.

Trump fired Bolton in September last year, over what he said had been disagreements with many of his suggestions.