"I know, I am certain, President Trump did not intend to attack the Chinese," the chairman of the Joint Chiefs of Staff told the Senate Armed Services Committee.

"My task at that time was to deescalate. My message again was consistent: stay calm and steady and deescalate. We are not going to attack you," he said.

The calls between Milley and his Chinese counterpart, General Li Zuocheng, were first revealed in the book "Peril" by Washington Post reporters Bob Woodward and Robert Costa.

The first call was on October 30, four days before the US presidential election, and the second was on January 8, two days after supporters of Trump stormed the US Capitol in an effort to prevent certification of Democrat Joe Biden's election victory.

Some Republican lawmakers have accused Milley of overstepping his authority and called for him to resign.

In his Senate testimony, Milley defended his actions and said the calls were coordinated with the then-secretaries of defense.

"The specific purpose of the October and January calls was generated by concerning intelligence which caused us to believe the Chinese were worried about an attack by the US," Milley said.

"These military-to-military communications at the highest levels are critical to the security of the United States in order to deconflict military actions, manage crisis, and prevent war between great powers armed with nuclear weapons," he said.

"At no time was I attempting to change or influence the process, usurp authority, or insert myself into the chain of command," Milley added.

"I firmly believe in civilian control of the military as a bedrock principle essential to this Republic and I am committed to ensuring the military stays clear of domestic politics."

- 'He doesn't launch them alone' -

Milley also addressed a phone call he had with Nancy Pelosi, the Democratic Speaker of the House of Representatives, in which -- according to "Peril" -- she sought reassurances that there was no danger of Trump unilaterally launching a nuclear strike.

"I sought to assure her that nuclear launch is governed by a very specific and deliberate process," Milley told the Senate committee.

"She was concerned and made various personal references characterizing the president," Milley said. "I explained that the president is the sole nuclear launch authority but he doesn't launch them alone."

According to the book, Pelosi, referring to Trump, said: "You know he's crazy. He's been crazy for a long time" and Milley responded: "Madam Speaker, I agree with you on everything."

In his testimony Milley said he told Pelosi that he was "not qualified" to determine a president's mental health.