CNN  — 

Gen. Mark Milley on Friday defended the calls he placed to his Chinese counterpart during Donald Trump’s final months in office as “perfectly within the duties and responsibilities” of his job as the chairman of Joint Chiefs of Staff, The Wall Street Journal reported.

“These are routine calls in order to discuss issues of the day, to reassure both allies and adversaries in this case, in order to ensure strategic stability,” Milley told reporters traveling with him on a military jet, the newspaper reported.

Milley made two backchannel calls to China’s top general, Li Zuocheng, that were revealed in “Peril,” the forthcoming book by Washington Post reporters Bob Woodward and Robert Costa that details the final days of the Trump presidency. In October, as intelligence suggested China believed the US was going to attack them, Milley sought to calm Li by reassuring him that the US was not considering a strike, according to the book. Milley called again two days after the January 6 riot at the US Capitol to tell Li that the US is “100 percent steady” even though “things may look unsteady.”

The top US defense official’s actions, which were reported by CNN and others this week ahead of the book’s release, drew sharp criticism from Trump and his allies, including calls for Milley’s resignation and that he be tried for treason, while the White House and current and former defense officials defended him.

Milley’s comments Friday are his first public response to the matter and come ahead of a September 28 hearing before the Senate Armed Services Committee, where he is sure to face questions about his actions in the final days of the Trump administration.

“I will go into any level of detail Congress wants to go into,” Milley told reporters, adding that he wants to wait to testify before Congress to provide more clarity rather than use the media to defend himself, according to the Journal.

On Wednesday, several current and former defense officials rejected the criticism that Milley was acting in secret or out of authority, saying that the calls were conducted under protocols similar to other high-level engagements by the Joint Chiefs chairman and in consultation with the Defense Department.

More than a dozen people were on both videoconference calls Milley held with Li, including a representative from the State Department, a defense official had told CNN. The read-out and notes from the calls were shared with the intelligence community and the interagency, the official said.

Milley conducted the October 30 call in consultation with then-Defense Secretary Mark Esper, but former acting Defense Secretary Chris Miller told CNN on Wednesday he wasn’t told the extent of Milley’s engagement with the Chinese on January 8 and that he “wouldn’t have approved of anything of the nature portrayed” in the book.

Milley’s spokesman, Col. Dave Butler, said Milley’s calls with other chiefs of defense “remain vital to improving mutual understanding of US national security interests, reducing tensions, providing clarity and avoiding unintended consequences or conflict.”

“His calls with the Chinese and others in October and January were in keeping with these duties and responsibilities conveying reassurance in order to maintain strategic stability,” he said in a statement Wednesday.

Milley is also facing criticism from Trump and his GOP allies for convening a secret meeting after January 6, in which the Joint Chiefs chairman instructed top military officers to consult him before proceeding with any order to take military action, including launching nuclear weapons.

The meeting was also detailed in “Peril,” which is based on more than 200 interviews with firsthand participants and witnesses.

This story has been updated.

CNN’s Katie Bo Williams and Jeremy Herb contributed to this report.