The US Food and Drug Administration(FDA) on Sunday has given emergency authorization for the use of blood plasma as a treatment against COVID-19.

The announcement came a day after Trump accused the FDA of impeding the rollout of vaccines and therapeutics for political reasons and on the eve of the Republican National Convention, where Trump will launch his campaign to win a second term in the White House.

"This product may be effective in treating COVID-19 and... the known and potential benefits of the product outweigh the known and potential risks of the product," FDA said in a statement.

Trump said it was "only made possible because of Operation Warp Speed", while adding, "We are years ahead of approvals. If we went by the speed levels of the past administration, it would be 2-3 yrs behind where we're today."

Trump also said the treatment could reduce deaths by 35%.

The FDA had already approved the use of plasma transfusions on coronavirus patients under certain conditions, like those who are gravely ill or taking part in clinical trials.

The United States is the worst-hit country with the virus accounting for over 176,700 deaths and more than 5.7 million infected cases.