The office of America's top general has pushed back against a report in a new book that he went around the nation's civilian leaders to place secret calls to his Chinese counterpart over concerns about then-President Donald Trump.

According to excerpts of the book, General Mark Milley, chairman of the Joint Chiefs of Staff, secretly called General Li Zuocheng of the People's Liberation Army twice to say that the US was stable and not going to attack and, if there were to be an attack, he would alert him ahead of time.

The excerpts were reported by the Washington Post yesterday.

"All calls from the chairman to his counterparts, including those reported, are staffed, coordinated and communicated with the Department of Defense and the interagency," Colonel Dave Butler, a spokesman for Milley, said in a statement.

"General Milley continues to act and advise within his authority in the lawful tradition of civilian control of the military and his oath to the Constitution," Mr Butler said.

President Joe Biden insisted that he had complete confidence in Milley's leadership.

Mr Biden said: "I have great confidence in General Milley."

Colonel Dave Butler said that Milley's calls with Chinese and others in October and January were "in keeping with these duties and responsibilities conveying reassurance in order to maintain strategic stability."

The book, "Peril," by journalists Bob Woodward and Robert Costa, which they said relied on interviews with 200 sources, is due to be released next week.

In a statement yesterday, Donald Trump called the story "fabricated." If it was true, he said, Mark Milley should be tried for treason.

"For the record, I never even thought of attacking China," Mr Trump said.

He appointed Mark Milley to the top military post in 2018 but began criticising him, as well as other appointees and former staffers, after losing the presidential election to Joe Biden in November 2020.

Republican Senator Marco Rubio called on Joe Biden to fire Mark Milley immediately.

According to the Washington Post, the book also said that Mr Milley called senior officers to review the procedures for launching nuclear weapons and told them that while the president alone could give an order to use them, he had to be involved.

"The meeting regarding nuclear weapons protocols was to remind uniformed leaders in the Pentagon of the long-established and robust procedures in light of media reporting on the subject," Mr Butler said.