US President Donald Trump has said a sobering warning by his top infectious diseases expert about lifting pandemic restrictions too soon was unacceptable.
He accused Dr Anthony Fauci of wanting "to play all sides of the equation" in his testimony to lawmakers on Tuesday.
The president said he was especially dissatisfied with Dr Fauci's caution around reopening schools too quickly.
Covid-19 has infected nearly 1.4 million people in the US and killed 84,000, while ravaging the economy.
What did the US president say?
Speaking on Wednesday at the White House, Mr Trump took issue with Dr Fauci's comments to a Senate hearing a day earlier about the risks to children of reopening and his assessment that a vaccine was unlikely before classes could begin this autumn.
"Look, he wants to play all sides of the equation," Mr Trump said of his top coronavirus expert's concerns.
"I was surprised by his answer actually, because, you know, it's just to me - it's not an acceptable answer, especially when it comes to schools," the president told reporters.
He said "the only thing that would be acceptable" is giving older teachers and professors a few more weeks before they return.
"Because this is a disease that attacks age, and it attacks health," the president said.
"But with the young children, I mean, and students, it's really - just take a look at the statistics. It's pretty amazing," Mr Trump added.
The Republican president is keen to get Americans back to work and has praised governors who are moving to do so while criticising others for not acting aggressively enough.
The country is split over Mr Trump's focus on protecting livelihoods, and critics accuse him of gambling with lives to serve his own political interests ahead of November's re-election bid.
The president's latest comments come amid reports of some young children being severely affected by an inflammatory syndrome that could be linked to the virus.
What did Dr Fauci say?
Speaking to lawmakers on Tuesday, the White House task force coronavirus expert warned that relaxing stay-at-home rules too quickly could bring more "suffering and death".
The director of the US National Institute of Allergy and Infectious Diseases emphasised the importance of not being "cavalier in thinking that children are completely immune to the deleterious effects" of the disease.
Dr Fauci said: "We just have to see on a step-by-step basis as we get into the period of time with the fall, about reopening the schools, exactly where we will be in the dynamics of the outbreak."
The infectious disease chief also said the real US death toll is probably higher than the official figure.
What's the national picture?
On Wednesday, Maryland's Governor Larry Hogan said he was lifting that state's stay-at-home measure, replacing it on Friday with a "safer-at-home" order.
The Republican, who has been critical of Mr Trump, cited a two-week decline in severe cases and deaths that federal guidelines recommend.
On Wednesday, Wisconsin's Supreme Court overturned Democratic Governor Tony Evers' stay-at-home order, ruling it "unenforceable" and "unlawful" in a victory for the Republican-led legislature.
A majority of states have begun a phased reopening approach. In some, like Texas and Georgia, public spaces and businesses have also been allowed to reopen.
New York, California, Washington DC, New Jersey and Illinois are among those with shutdowns still in place.