Image provided by the White House shows U.S. President Donald Trump participating in a phone call with Vice President Mike Pence, Secretary of State Mike Pompeo, and Chairman of the Joint Chiefs of Staff General Mark Milley from a conference room at Walter Reed National Military Medical Center in Bethesda, Maryland, the United States, on Oct. 4, 2020. White House chief of staff Mark Meadows was also in the room, but not pictured, according to the White House. (Photo: Xinhua)

WASHINGTON, Oct. 5 (Xinhua) -- U.S. President Donald Trump appeared eager for a quick return on Sunday as he's undergoing COVID-19 treatment at a hospital despite concern about his condition.

Sunday evening, Trump briefly left his suite at Walter Reed National Military Medical Center in Bethesda, Maryland for a motorcade ride to greet his supporters outside the hospital. The masked president, accompanied by Secret Service agents, waved and gave a thumbs up from the backseat of a black SUV.

"I'm not telling anybody but you, but I'm about to make a little surprise visit," the president said in a video posted to Twitter before going out for the greeting.

The movement immediately raised safety concern as critics argued Trump, who's still recovering from the highly contagious virus, was unnecessarily putting his security detail at risk.

"That Presidential SUV is not only bulletproof, but hermetically sealed against chemical attack. The risk of COVID-19 transmission inside is as high as it gets outside of medical procedures," James Phillips, an attending physician at Walter Reed, tweeted. "The irresponsibility is astounding. My thoughts are with the Secret Service forced to play."

White House deputy press secretary Judd Deere defended the drive-by, claiming in a statement that it "was cleared by the medical team as safe to do."

"Appropriate precautions were taken in the execution of this movement to protect the President and all those supporting it, including PPE," Deere added.

Earlier on Sunday, a day after Trump's doctors said he has been "not yet out of the woods," they provided a rosy assessment of his condition, saying that the president could be discharged as early as Monday.

"If he continues to look and feel as well as he does today, our hope is that we can plan for a discharge as early as tomorrow to the White House where he can continue his treatment course," Brian Garibaldi, a member of Trump's medical team and lung specialist, briefed reporters from Walter Reed.

Trump participated in a phone call with Vice President Mike Pence, Secretary of State Mike Pompeo, and Chairman of the Joint Chiefs of Staff General Mark Milley from a conference room at Walter Reed on Sunday, according to the White House.

"So far the president is in great shape. He's firmly in command of the government of the country," U.S. National Security Advisor Robert O'Brien told CBS News earlier in the day, calling a transfer of power from Trump to Pence not "on the table right now."

Trump was first diagnosed with COVID-19 on Thursday and moved to Walter Reed on Friday, where he was using Remdesivir, a COVID-19 drug made by the U.S. biopharmaceutical company Gilead Sciences, as a treatment. The president also received a dose of an experimental antibody cocktail being developed by U.S. drug maker Regeneron.

CONDITION REMAINS UNCLEAR

On Sunday, White House physician Sean Conley disclosed Trump, whose condition "has continued to improve" though he experienced two transient drops in his oxygen levels, had been additionally given a dose of dexamethasone, an anti-inflammatory steroid typically used by some severely ill COVID-19 patients.

The U.S. National Institutes of Health's COVID-19 treatment guidelines stated dexamethasone should be given only to patients who are on ventilators or need supplemental oxygen, while recommending against it for those with less serious illness because of the potential for harm.

Trump, aged 74 and clinically obese, is at a higher risk of serious complications from COVID-19 that has infected more than 7.4 million people and killed nearly 210,000 in the United States.

Conley confirmed on Sunday that Trump was given supplemental oxygen for about an hour on Friday before he was flown to hospital.

"Late Friday morning when I returned to the bedside, the president had a high fever and his oxygen saturation was transiently dipping below 94 percent," he said. "Given these developments I was concerned for possible rapid progression of the illness. I recommended the president we try supplemental oxygen, see how he would respond." Normal oxygen saturation levels are over 95 percent.

When pressed by reporters why it took him so long to reveal that information, Conley said that he was trying to "reflect the upbeat attitude" that the team and president have had over the course of his illness.

"I didn't want to give any information that might steer the course of illness in another direction, and in doing so it came off that we were trying to hide something, which wasn't necessarily true," he added.

The remarks came a day after a source familiar with Trump's health, later identified by U.S. media outlets as White House chief of staff Mark Meadows, spoke with reporters on background to offer a more worrisome portrayal of the president's condition.

"The president's vitals over the last 24 hours were very concerning," the official said in comments passed along to the media by a member of the White House press pool on Saturday. "The next 48 hours will be critical in terms of his care. We're still not on a clear path to a full recovery."

Trump is reportedly furious with Meadows over the statement, which has created confusion over the president's health and led to calls for more information and transparency from the White House.

"When you don't have full transparency, when there's cover-ups, contradictory statements, even lying about something as vital to the nation's security as the President's health, the nation is severely endangered," U.S. Senate Minority Leader Chuck Schumer, a New York Democrat, said on Sunday.

Conley insisted on Sunday that Meadows's remarks had been "misconstrued."

"What he meant was that 24 hours ago, when he and I were checking on the president, that there was that momentary episode of the high fever and that temporary drop in the saturation, which prompted us to act expediently to move him up here," Conley said. "Fortunately, that was really a very transient, limited episode."

It is not yet clear when and how Trump infected with COVID-19. The president announced his infection early Friday morning shortly after confirming White House counselor Hope Hicks, who had traveled with him multiple times the past several days, had caught the virus.

Before the diagnosis, Trump had a packed schedule, including hosting a ceremony to introduce a Supreme Court nominee at the White House Rose Garden, traveling to Cleveland, Ohio for the first 2020 presidential debate, addressing a rally in Duluth, Minnesota, and attending a fundraiser at his New Jersey golf club.