US President Donald Trump's condition is improving as he is being treated for Covid-19 at a military hospital, and he could return to the White House as early as Monday, where his treatment would continue, the doctors leading his treatment said on Sunday.

Doctors provided Trump supplemental oxygen twice during his battle with the lung disease, on Thursday and Friday, and have also given him dexamethasone, they told reporters the day after a series of contradictory messages from the White House caused widespread confusion about Trump's condition.

Dexamethasone is shown in studies to improve survival for patients hospitalized with critical Covid-19 who need extra oxygen. But it should not be given in mild cases since it can limit the body's own ability to combat the virus, according to guidelines from the Infectious Disease Society of America.

"The fact of the matter is that he's doing really well," Dr. Sean P. Conley told reporters at Walter Reed National Military Medical Center, where Trump has been receiving treatment since Friday.

Doctors said Trump has not run a fever since Friday and that his liver and kidney function remained normal after the second dose in a five-day course of Remdesivir, an intravenous antiviral drug sold by Gilead Sciences Inc <GILD.O> that has been shown to shorten hospital stays.