Joint Chiefs Chair General Mark Milley ordered aides to not act immediately on any move by Trump to use US nuclear forces, and he called a Chinese general to reassure Beijing, presidential chronicler Bob Woodward and co-author Robert Costa wrote in their soon-to-be-released book.

The Washington Post -- Woodward's and Costa's employer -- and CNN on Tuesday reported excerpts from the book "Peril," depicting Milley as organizing the Pentagon and intelligence community to resist any move by Trump to ratchet up tensions with China after he lost the November 2020 presidential election.

Milley called Chinese counterpart General Li Zuocheng twice, on October 30 just before Trump's election defeat, and on January 8, two days after Trump supporters attacked the US Capitol, to reassure him that the Republican president's anti-China rhetoric could not translate into military action.

"General Li, I want to assure you that the American government is stable and everything is going to be okay," Milley told Li in the October call, Woodward and Costa write.

"We are not going to attack or conduct any kinetic operations against you," Milley said.

- Nuclear strike worries -

Two months later, Milley used the secret back-channel with Li again after the US Capitol riot, amid concerns both in Beijing and Washington that Trump was unstable.

"We are 100 percent steady. Everything's fine. But democracy can be sloppy sometimes," Milley told Li, according to the book.

To reassure the Chinese, Milley went so far as to have the Pentagon's Indo-Pacific Command postpone military exercises that Beijing might have viewed as a possible threat.

Separately, Milley told his top staff that if Trump sought to exercise his power to order a nuclear strike, that they had to inform him first.

And Milley discussed with other top officials, including CIA director Gina Haspel and National Security Agency head Paul Nakasone, the need to be vigilant amid concerns Trump could act irrationally.

"Some might contend that Milley had overstepped his authority and taken extraordinary power for himself," the authors wrote.

But he believed he was acting correctly "to ensure there was no historic rupture in the international order, no accidental war with China or others, and no use of nuclear weapons," they said.

The Pentagon declined to comment on the book's claims.

Milley and others, including Haspel, were worried that Trump would undertake an attack on China or Iran out of frustration or to find a way to hold onto the presidency.

"This is a highly dangerous situation. We are going to lash out for his ego?" said the CIA chief, according to the book.

- 'He's crazy' -

Milley's second Li call came after the top lawmaker in Congress, House of Representatives Speaker Nancy Pelosi, phoned Milley about Trump's state of mind and his rejection -- held to this day -- of President Joe Biden's election victory.

Two days earlier, goaded on by Trump, hundreds of supporters violently stormed Congress, forcing lawmakers to cancel a session meant to certify Biden's victory and forcing lawmakers of both parties to flee.

Woodward and Costa obtained a transcript of the Pelosi call.

"What precautions are available to prevent an unstable president from initiating military hostilities or from accessing the launch codes and ordering a nuclear strike?" Pelosi asked.

"If they couldn't even stop him from an assault on the Capitol, who even knows what else he may do?" she said.

"He's crazy. You know he's crazy... and what he did yesterday is further evidence of his craziness."

The system had "a lot of checks" to forestall extreme behavior by the president, Milley responded.

Nevertheless, he said, "I agree with you on everything."