US General Mark Milley, the top US military officer, has defended calls with China that have raised Republican demands for his resignation, saying he had been aiming to ease tension with Beijing and not to "usurp authority".

The remarks were Gen Milley's first detailed defence of his actions since a book detailed what it described as "secret" calls with General Li Zuocheng of the People's Liberation Army on 30 October 2020 and again on 8 January.

The book cited Beijing's concerns that then-president Donald Trump could spark a war with China as his potential election loss loomed, and in its aftermath.

Gen Milley broadly confirmed the premise of the account but dismissed the idea that the calls were secret, saying they had been coordinated with the US government.

"I know, I am certain, President Trump did not intend on attacking the Chinese and it is my directed responsibility to convey presidential orders and intent," Gen Milley told the Senate Armed Services Committee.

"My message again was consistent: calm, steady, de-escalate. 'We are not going to attack you'."

US President Joe Biden has supported Gen Milley throughout the controversy surrounding the calls, saying he had "great confidence" in him.

It is the latest controversy surrounding the top US military officer, who caused an uproar last year after accompanying Mr Trump toward a church for a photo opportunity after authorities cracked down on civil rights protesters.

Mark Milley with Donald Trump

He later said he regretted it, saying it created a perception of a military involved in domestic politics.

Gen Milley publicly confirmed intelligence that caused US officials to believe China was "worried about an attack" by the United States.

Gen Milley acknowledged that he spoke on 8 January with US House of Representatives Speaker Nancy Pelosi, who, according to the Washington Post, had asked the general what safeguards were in place to prevent an "unstable president" from launching a nuclear strike.

"He's crazy. You know he's crazy," Ms Pelosi told Gen Milley, the newspaper reported, citing a transcript of the call.

Gen Milley, in his remarks to Congress, said Ms Pelosi had asked him on 8 January about whether Mr Trump's actions might lead to an accidental nuclear missile launch.

He responded by assuring her of safeguards and added: "I am not qualified to determine the mental health of the president of the United States."

Gen Milley told the Senate Armed Services Committee: "At no time was I attempting to change or influence the process, usurp authority, or insert myself into the chain of command."

Mr Trump, in a statement, has said he "never even thought of attacking China". But after the initial account of Gen Milley's calls with China surfaced, Mr Trump said Gen Milley should be fired if they were true.

Republican Senator Marco Rubio has called for Gen Milley's resignation. Senator Rand Paul said he should be prosecuted if the account in the book was true.

Some of the strongest concerns have come from politicians in the House, where Gen Milley will testify tomorrow.