The National Security Council said the manuscript of former national security adviser John Bolton’s forthcoming book contains “significant amounts” of classified information and can’t be published in its current form, according to a letter the council sent to Mr. Bolton’s lawyer.

“Under federal law and the nondisclosure agreements your client signed as a condition for gaining access to classified information, the manuscript may not be published or otherwise disclosed without the deletion of this classified information,” said the letter, dated Jan. 23, a copy of which was reviewed by The Wall Street Journal. The letter was signed by Ellen Knight, senior director for Records, Access and Information Security Management at the NSC.

Mr. Bolton’s book, “The Room Where It Happened: A White House Memoir,” is expected to go on sale on March 17, and will be published by Simon & Schuster, a unit of ViacomCBS Inc.

On Sunday, the New York Times published details of the manuscript, including that Mr. Bolton alleges President Trump told him in August that he wanted to keep aid to Ukraine frozen until the country aided investigations into Democrats, including former Vice President Joe Biden, one of Mr. Trump’s top 2020 rivals, and Mr. Biden’s son. Chuck Cooper, Mr. Bolton’s lawyer, confirmed the report.

The claim goes to the heart of Democrats’ case for impeachment and contradicts the White House’s argument that the decision to hold up nearly $400 million in aid to Ukraine wasn’t related to the president’s push for investigations there.