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.

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.

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.