The head of the US agency in charge of developing a vaccine against coronavirus said on Wednesday that he was removed from his job for opposing the chloroquine treatment promoted by US President Donald Trump.

Dr Rick Bright said he was removed on Tuesday as director of the Biomedical Advanced Research and Development Authority, the government agency for developing and procuring treatments and vaccines, and moved to a lesser position in the National Institutes of Health.

"I believe this transfer was in response to my insistence that the government invest the billions of dollars allocated by Congress to address the Covid-19 pandemic into safe and scientifically vetted solutions, and not in drugs, vaccines and other technologies that lack scientific merit," he said in a statement to US media.

He said the move was a direct response to his resistance to "misguided directives" to support the use of malaria treatments chloroquine and hydroxychloroquine for coronavirus.

Those treatments, he said, were "promoted by the administration as a panacea," but "clearly lack scientific merit".

"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."

Since mid-March Trump, backed by the conservative Fox News channel, has advocated for the use of chloroquine to treat Covid-19 infections, with scant evidence from studies of its safety or effectiveness.

Read: Doctors embrace drug touted by Trump for Covid-19, without hard evidence it works

Despite his own science advisors suggesting more study is needed, Trump repeatedly pushed for the drugs' use, claiming the treatment could be a "gift from God" to counter the coronavirus pandemic.

On Tuesday the results of the largest study yet of hydroxychloroquine, funded by the US government, showed no benefit against the disease over standard care.

And in fact it showed use of hydroxychloroquine was associated with more deaths.

Bright said he would be asking the inspector general of the Department of Health and Human Services to investigate the Trump administration's politicisation of of the agency and its pressuring scientists to favor companies with political connections.

"Sidelining me in the middle of this pandemic and placing politics and cronyism ahead of science puts lives at risk and stunts national efforts to safely and effectively address this urgent public health crisis," he said.