The lawsuit had sought to recover money Bolton made from the book, according to a court document filed in federal court in the District of Columbia.

The book, The Room Where It Happened: A White House Memoir, was highly critical of Trump, who had fired Bolton in September 2019 after roughly 17 months as national security adviser.

"By ending these proceedings without in any way penalising Ambassador Bolton or limiting his proceeds from the book, the Department of Justice has tacitly acknowledged that President Trump and his White House officials acted illegitimately," Bolton lawyer Charles Cooper said on Wednesday.

Sarah Tinsley, a spokeswoman for Bolton, said the reversal was a "complete vindication" for the former US ambassador to the United Nations.

A Justice Department spokesperson did not immediately respond to a request for comment.

The book, released in the run-up to the 2020 presidential election, offered a behind-the-scenes, and unflattering, account of Trump's foreign policy dealings.

It described how Trump asked China's President Xi Jinping to help the American's re-election prospects and how Trump had pressured his Ukraine counterpart for politically charged investigations.

Trump's Justice Department argued the book contained classified information that could threaten national security.

After losing its request for an injunction, the department pursued a civil lawsuit seeking to recover proceeds from the memoir's sales.

It launched a criminal investigation last September into whether Bolton mishandled classified information when he published the book.

Prosecutors had issued grand jury subpoenas seeking information from Bolton's literary agent, Javelin, and Simon & Schuster.

Australian Associated Press