WASHINGTON (REUTERS) - The US top general secretly called his Chinese counterpart twice last year over concerns then-president Donald Trump could spark a war with China as his potential election loss loomed and in its aftermath, The Washington Post reported on Tuesday (Sept 14).

US General Mark Milley, chairman of the Joint Chiefs of Staff, called General Li Zuocheng of the People's Liberation Army on Oct 30, 2020 - four days before the presidential election - and again on Jan 8, two days after Trump supporters led a deadly riot at the US Capitol, the paper reported.

In the calls, Gen Milley sought to assure Gen Li the United States was stable and not going to attack and, if there were to be an attack, he would alert his counterpart ahead of time, the report said.

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

Mr Trump said in an interview with news website Newsmax on Tuesday that Gen Milley's reported promise to give Gen Li advance warning of any attack was "treasonous" and that there was no need for such a call.

"I did not ever think of attacking China," Mr Trump said.

Gen Milley's office declined to comment.

Republican Senator Marco Rubio called on President Joe Biden, a Democrat, to immediately fire Gen Milley.

"I do not need to tell of you the dangers posed by senior military officers leaking classified information on US military operations, but I will underscore that such subversion undermines the President's ability to negotiate and leverage one of this nation's instruments of national power in his interactions with foreign nations," Mr Rubio said in a letter to Mr Biden.

Asked about the report by reporters travelling with Mr Biden aboard Air Force One, White House spokesman Karine Jean-Pierre declined to comment and referred them to the Joint Chiefs of Staff and the Defence Department.

The Republican Trump named Gen Milley to the top military post in 2018 but began criticising him after losing the November election to Mr Biden and left the White House on Jan 20.

Gen Milley was motivated to contact Beijing the second time in part due to a Jan 8 call with House Speaker Nancy Pelosi, who had asked the general what safeguards were in place to prevent an "unstable president" from launching a nuclear strike, the report said, citing a transcript of the call.

"He's crazy. You know he's crazy," Ms Pelosi told Gen Milley in the call, according to the report.

According to the cited call transcript, the general replied: "I agree with you on everything."