More than 15 months after the start of the coronavirus pandemic, the U.S. military’s top officer says the evidence of its origin remains "inconclusive" but says a "cover-up," by the Chinese government isn’t helping find the answer.

Aboard a military aircraft returning from the Air Force Academy late Wednesday, Gen. Mark Milley, chairman of the Joint Chiefs of Staff, was asked by Fox News if his opinion had changed from over a year ago when he said "The weight of evidence seems to indicate natural, but we don’t know for certain."    

"My opinion hasn't changed, because I haven't seen any different evidence," Milley said. "What I said a year ago, it's still true today. It's inconclusive, we don't know."

Milley says the reason the world still doesn’t know the origin of the coronavirus is because of the Chinese communist government.

WHITE HOUSE WON'T SAY IF CHINA WILL BE PUNISHED IF LAB LEAK THEORY IS PROVEN

"Once this virus started appearing, there seems to have been a fair amount of activity or cover-up or lack of transparency, probably the best way to put it, and all of that is disturbing. So we need to get to the bottom of it. That’s clear."

Milley added, "I think that the president is exactly right, we need to get to the bottom of it." 

Milley’s plane landed at Andrews Air Force Base outside the nation’s capital around the same time the U.S. Senate passed a bill that would require the Biden administration and the director of national intelligence to declassify intelligence on the origins of COVID-19.

A view of the P4 lab inside the Wuhan Institute of Virology after a visit by the World Health Organization team in Wuhan in China's Hubei province on Wednesday, Feb. 3, 2021. (AP Photo/Ng Han Guan)

A view of the P4 lab inside the Wuhan Institute of Virology after a visit by the World Health Organization team in Wuhan in China's Hubei province on Wednesday, Feb. 3, 2021. (AP Photo/Ng Han Guan) ((AP Photo/Ng Han Guan))

Earlier Wednesday, President Biden said U.S. intelligence were weighing two possible scenarios – that the virus either leapt to a human from contact with an infected animal or that it accidentally leaked from a laboratory in Wuhan, China.

FAUCI PRAISES ‘COMPETENT, TRUSTWORTHY' CHINESE SCIENTISTS

Nicholas Wade, a former staff writer for the New York Times science section, said earlier this month the World Health Organization commission sent to China in February to investigate the origins of the virus was "heavily controlled" by the Chinese government. 

Wade doubts the pandemic spread naturally. 

"What became clear was that the Chinese had no evidence to offer the commission in support of the natural emergence theory," Wade said. 

But Wade admits, "Neither the natural emergence nor the lab escape hypothesis can yet be ruled out. There is still no direct evidence for either. So no definitive conclusion can be reached."

According to a fact sheet issued by the State Department five days before Biden's inauguration, "The U.S. government has reason to believe that several researchers inside the [Wuhan Institute of Virology] became sick in autumn 2019, before the first identified case of the outbreak, with symptoms consistent with both COVID-19 and common seasonal illnesses."

The U.S. says this statement was crafted from declassified intelligence reports at the end of the Trump administration.

Milley says the origin of the virus must be discovered. 

"We need to know as a nation," he said. "We need to know as a world, because the scale and scope of this pandemic was enormous. It still is enormous." 

CLICK HERE TO GET THE FOX NEWS APP

"The failure to get our inspectors on the ground in those early months will always hamper any investigation into the origin of COVID-19," Biden said Wednesday. 

Biden asked the intelligence agencies to "redouble" their efforts in finding the origins of the coronavirus and to report back to him in 90 days. 

Milley gave the commencement address at the Air Force Academy, where he warned of the growing rift between the U.S. and China and Russia.

"We are now in the 76th year of the great power peace following World War II. And it is under stress," Milley told the 1,019 Air Force Academy graduates and their families in Colorado Springs, Colo. "We can see it fraying at the edge."

"Right now we are in a great power competition with China and Russia. And we need to keep it at competition and avoid great power conflict," he added.