The NSC said its review of the forthcoming memoir contained “significant amounts of classified information.”

The White House sent a letter last week to John Bolton’s attorney informing him that Bolton’s forthcoming book revealing sensitive details about his conversations with President Donald Trump could not be published because it contained classified information.

An official with the National Security Council sent the letter on Jan. 23 to Charles Cooper, shortly before The New York Times published an explosive article detailing how Bolton planned to reveal that Trump directly tied the withholding of foreign aid to Ukraine as he pressured the country to launch investigations into his political rivals.

The letter states that Bolton’s manuscript for “The Room Where It Happened: A White House Memoir” contains “significant amounts of classified information.”

“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agreements your client signed as a condition for gaining access to classified information, the manuscript may not be published or otherwise disclosed without the deletion of this classified information,” Ellen Knight of the National Security Council Records Management Division wrote to Cooper.

The stern letter deepens the drama surrounding Bolton, whose revelations have injected uncertainty into the Senate impeachment trial of Trump. Republican senators who are seeking a quick acquittal of the president are now facing pressure from Democrats and a few Republicans to potentially hear from witnesses, including Bolton.

The manuscript for Bolton’s book has been under under review by the NSC’s Records Management Division for weeks, and Washington has been seized by a blame game over who leaked its details.

On Wednesday morning, the president fired off a series of tweets attacking Bolton and his book, which is scheduled to be published in March by Simon & Schuster. Trump called his book “nasty & untrue,” and said it was “All Classified National Security.”

News of the White House letter was first reported by CNN.

A spokesperson for Bolton and the White House did not immediately respond to a request for comment.