The US’s top military officer took secret action to limit former president Donald Trump’s ability to launch a military strike or deploy nuclear weapons, according to a new book.

Joint Chiefs Chairman General Mark Milley was worried Mr Trump would “go rogue” in the wake of the 6 January attack on the US Capitol.

It is among a number of explosive claims from the authors of Peril – a book by Washington Post journalists Bob Woodward and Robert Costa.

They write that Gen Milley was deeply disturbed by the attack on the Capitol and “was certain that Trump had gone into a serious mental decline in the aftermath of the election, with Trump now all but manic, screaming at officials and constructing his own alternate reality about endless election conspiracies.”

“You never know what a president’s trigger point is,” he allegedly told his staff, according to CNN.

In a bold move, the top military officer called a secret meeting in his Pentagon office on 8 January to review the processes for launching military action and nuclear weapons.

He allegedly told the officials in charge of the Pentagon’s war room, the National Military Command Center, to not take any orders unless he was involved.

Gen Milley told the officials: “No matter what you are told, you do the procedure. You do the process. And I’m part of that procedure”.

“Got it?” he asked, according to the book.

The officials are said to have replied “yes, sir” and the authors wrote that Gen Milley “considered it an oath”.

Details from the book, which will be released on 21 September, were first reported by The Washington Post on Tuesday.

It is based on more than 200 interviews with participants and witnesses to the covered events, giving an insight into Mr Trump’s erratic behaviour in his final days of office, which reportedly included shouting at his senior staff as he clung to power.

Gen Milley’s fear of what Mr Trump might do in his final weeks as president prompted him to twice call his Chinese counterpart, General Li Zuocheng, to assure him that the two nations would not suddenly go to war.

“General Li, I want to assure you that the American government is stable and everything is going to be okay,” Gen Milley told him in the first call on 30 October 2020, according to the book. “We are not going to attack or conduct any kinetic operations against you.”

“If we’re going to attack, I’m going to call you ahead of time. It’s not going to be a surprise,” Gen Milley reportedly said.

The second call was on 8 January 2021, just two days after the insurrection at the US Capitol by supporters of the outgoing president.

Mr Trump said Gen Milley should be tried for treason if the report was true.

The book also looks into Joe Biden’s decision to run for office again and examines the first six months of his presidency – and why he pushed so hard to withdraw from Afghanistan. It also discusses how he really feels about Mr Trump.