WASHINGTON (AFP) - The White House told former national security adviser John Bolton that a book reportedly containing damaging evidence for President Donald Trump cannot be published because it breaks secrecy laws.

The warning was made in a letter to Bolton's lawyer dated Jan 23 but only made public on Wednesday (Jan 29) as Trump's impeachment trial intensified in the Senate.

The National Security Council said after preliminary review of the manuscript - a vetting process applied to any White House employees writing books - that it contained "significant amounts of classified information".

"Some of this information is at the TOP SECRET level," the NSC said in a letter to Bolton's lawyer Charles Cooper, adding that "the manuscript may not be published or otherwise disclosed without the deletion of this classified information."

Democrats are pressing for the Senate to subpoena Bolton after reports that his White House memoir The Room Where it Happened corroborates the abuse-of-power impeachment charge against Trump.

Bolton reportedly writes that the president personally told him in August a freeze in military aid to Ukraine was directly linked to Trump's demand that Kiev announce investigations into Joe Biden, the frontrunner for the Democratic presidential nomination.

Several hours before the NSC letter went public, Trump lashed out at Bolton on Twitter, saying he had written a "nasty & untrue book. All Classified National Security."

Despite the formal review process of Bolton's book, drafts have already circulated around Washington, where the passages describing Trump's relationship with Ukraine caused a sensation.

At a news conference in Davos last week, Trump indicated he was worried about Bolton, whom he fired in 2019.

Trump said the veteran foreign policy adviser "knows some of my thoughts. He knows what I think about leaders. What happens if he reveals what I think about a certain leader and it's not very positive?"