Having resisted wearing a mask in the past, Trump has until recently denied the effectiveness of masks in curtailing the spread of the virus.
"I don't agree with the statement that if everyone wore a mask, everything disappears," he said in an interview with Fox News anchor Chris Wallace aired Sunday, confirming that he won't issue a national mask mandate.
The Monday tweet came as the confirmed cases in the United States surpassed 3.8 million and death toll topped 140,800, according to an update by Johns Hopkins University on Monday afternoon. Both of the figures are the world's largest, leading those of other nations by wide margins.
Earlier in the day, Trump told reporters that he would resume the daily coronavirus briefings at the White House, possibly as soon as 5 p.m. ET on Tuesday.
"I think it's a great way to get information out to the public as to where we are with the vaccine, with the therapeutics, and generally speaking where we are," Trump said. "So I think we'll start that, probably starting tomorrow."
Trump appeared at the briefings featuring the White House Coronavirus Task Force almost daily between March and April, before the gatherings at the White House West Wing came to a sudden halt.
Vice President Mike Pence and other task force members held the media sessions a few times during the past month when cases spiked sharply in the country.