The removed director of a key United States agency who was tasked with developing drugs to fight the coronavirus pandemic said on Wednesday he was dismissed because he called for the careful vetting of a treatment frequently touted by President Donald Trump.

Rick Bright said he was replaced as director of the Biomedical Advanced Research and Development Authority, or BARDA and reassigned to a new role because he resisted efforts to push hydroxychloroquine and the related chloroquine as cures for COVID-19, the respiratory illness caused by the coronavirus.

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"While I am prepared to look at all options and to think 'outside the box' for effective treatments, I rightly resisted efforts to provide an unproven drug on demand to the American public," Bright said in the statement, reported by multiple US media outlets on Wednesday.

Bright said the US government has promoted the medicines as a "panacea" even though they "clearly lack scientific merit."

Bright has retained a law firm, Katz, Marshall & Banks, known for representing whistleblowers.

The US Department of Health and Human Services, which oversees BARDA, said on Tuesday that Bright had been moved to a new public-private partnership under the National Institutes of Health announced last week.

The country's top infectious disease expert Dr Anthony Fauci said on Wednesday he had heard that in his new role, Bright would be responsible for the development of diagnostics, a "very, very important" issue.

BARDA officials did not immediately respond to a request for comment on Wednesday.

'I may take it'

Bright, an expert in vaccines and therapeutics, was named BARDA's director in 2016 before Trump took office as president.

Trump has repeatedly promoted chloroquine and hydroxychloroquine as potential treatments for COVID-19, including saying early this month, "I may take it," even though doctors said the drugs' effectiveness were unproven and further tests were required.

When asked about Bright's case at a media briefing on Tuesday, Trump said he was not familiar with the official.

"I never heard of him. A guy says he was pushed out of a job. Maybe he was maybe, he wasn't. You'd have to hear the other side," he said.

In the absence of any known effective treatments, doctors on the front lines said they began using hydroxychloroquine and chloroquine on deteriorating patients based on a few small studies suggesting a possible benefit. Some said they had come under pressure from patients to use the therapies widely touted by Trump and other supporters.

After Reuters news agency reported on that pattern, the US Centers for Disease Control and Prevention removed from its website highly unusual guidance informing doctors on how to prescribe the drugs.