Former Acting Secretary of Defense Christopher Miller, who served in the final months of President Donald Trump’s term, said he “did not and would not ever authorize” Chairman of the Joint Chiefs of Staff Gen. Mark Milley’s “secret” communications with a Chinese official and called on him to resign “immediately” from the Biden administration.

The explosive allegations against Milley represent a “disgraceful and unprecedented act of insubordination,” Miller told Fox News in a statement on Wednesday.

“The Chairman of the Joint Chiefs of Staff is the highest-ranking military officer whose sole role is providing military-specific advice to the president, and by law is prohibited from exercising executive authority to command forces,” the former Trump official continued. “The chain of command runs from the President to the Secretary of Defense, not through the Chairman.”

“Pursuit of partisan politics and individual self-interests are a violation of an officer’s sacred duty and have no place in the United States military,” Miller added, noting that “a lesser ranking officer accused of such behavior would immediately be relieved of duty pending a thorough and independent investigation. As secretary of defense, I did not and would not ever authorize such conduct.”

According to the forthcoming book “Peril,” authored by Washington Post reporters Bob Woodward and Robert Costa, Milley warned China’s Gen. Li Zuocheng that he would provide advance warning if President Trump ordered an attack on the communist regime. Milley made two calls to Zuocheng, one on October 30th, 2020 and the other on January 8th, 2021. Additionally, Woodward and Costa claim that Milley believed that Trump was in mental decline, a viewpoint he conveyed to House Speaker Nancy Pelosi (D-CA) during a January 8th phone call. Pelosi is said to have agreed with Milley’s assessment.

Trump responded Tuesday with a sharply worded statement dismissing Milley as a “Dumbass,” and insisting he never considered attacking China.

Still, he said that if the report was true, “I assume he would be tried for TREASON in that he would have been dealing with his Chinese counterpart behind the President’s back and telling China that he would be giving them notification ‘of an attack.’ Can’t do that!”

The Associated Press contributed to this report.