US Food and Drug Administration (FDA) Commissioner Stephen Hahn has declined to back President Donald Trump's claim that 99 per cent of COVID-19 cases were "totally harmless".
During his remarks on Saturday at the White House Independence Day event, Trump had claimed without evidence that 99 per cent of coronavirus cases "are totally harmless."
When pressed in a CNN interview on Sunday to respond to Trump's remarks, Hahn refused to answer and instead said: "I'm not going to get into who is right and who is wrong," Xinhua news agency reported.
Hahn said the coronavirus pandemic is "a rapidly evolving situation" but stressed that the US "absolutely must take this seriously".
"What I'll say is that we have data in the White House task force. Those data show us that this is a serious problem. People need to take it seriously," he added.
Also on Sunday, Hahn refused to offer a timeline for a COVID-19 vaccine, which Trump suggested could be available "long before the end of the year".
"I can't predict when a vaccine will be available," the FDA chief said.
"We are seeing unprecedented speed for the development of a vaccine. But ... our solemn promise to the American people is that we will make a decision based upon the data and science on a vaccine, with respect to the safety and effectiveness of that vaccine."
Hahn's remarks came as COVID-19 cases have surged in recent weeks in more than 30 US states including Arizona, California, Texas and Florida.
According to the latest tally by Johns Hopkins University, the US currently accounts for the world's highest number of infections and fatalities with 2,880,130 and 129,906, respectively.