Donald Trump has claimed Boris Johnson's early approach to the coronavirus outbreak would have been 'very catastrophic' for the UK if he had not changed tack.
The US President suggested the Prime Minister had initially looked to 'ride out' the virus in an approach which would have caused 'a lot of death'.
Mr Trump's press conference criticism appeared to be a reference to the claim that the UK had previously been following a plan for so-called 'herd immunity'.
Mr Trump's remarks came as the UK's coronavirus death toll hit 2,352 with 29,474 people now having tested positive.
Donald Trump, pictured in the White House on March 2, said Boris Johnson's original approach to tackling coronavirus would have been 'very catastrophic' for the UK
Mr Johnson has been conducting all government business using video conferencing software since his positive test last week
Sir Patrick Vallance, the UK's chief scientific adviser, told the BBC on March 13 that the 'aim' was to 'not suppress (coronavirus) completely... to build up some kind of herd immunity so more people are immune to this disease'.
He suggested that could take place while also trying to reduce the peak number of infections to protect the NHS.
The concept would likely have seen the elderly and vulnerable shielded from Covid-19 but those deemed fit would have been free to contract the illness in a bid to build up nationwide immunity.
But a week after 'herd immunity' was mentioned by the adviser, Mr Johnson, who last week tested positive for coronavirus, opted to put the UK on lockdown after seeing expert modelling which forecast 250,000 deaths unless stringent social distancing restrictions were imposed.
Speaking during a two-hour White House briefing, Mr Trump said: 'A lot of people were saying, "Let's just ride it out".
'This is not to be ridden out. Then you would have been looking at 2.2 million people (dying in the US) in a relatively short period of time.
'If you remember, they were looking at that concept - I guess it is a concept, if you don't mind death, a lot of death.
'But they were looking at that concept in the UK, remember? They were very much looking at it.
'All of a sudden they went hard the other way because they started seeing things that weren't good. They put themselves in a little bit of a problem.
'Now Boris has tested positive and I hear - I hope - he's going to be fine.
'But in the UK they were looking at that - they have a name for it but we won't even go by the name - (and) it would have been very catastrophic I think if that had happened.'
The Republican president said 'doing nothing' to tackle coronavirus could cost as many as 2.2 million lives in the United States, rather than the estimated 100,000 to 200,000 currently predicted to die - even with social distancing measures in place until April 30.
Mr Trump recently changed his own approach to the crisis.
A little over a week ago, the President vowed 'never to turn the country off' as he suggested the Covid-19 death toll was unlikely to be worse than for flu.
But he told reporters yesterday that coronavirus was 'probably the worst thing the country has ever seen' and predicted worse casualties than in the First World War for the US.
Asked by reporters whether he planned to travel while the Stateside restrictions were in force, the 73-year-old said he would be remaining in Washington, highlighting Mr Johnson's development of the illness.
The PM is self-isolating in Downing Street after testing positive on Friday.
Mr Trump said: 'I'd love to go out but no, I'll be in the White House.
'I think it is important - you saw what happened with Boris Johnson, you've seen what happened with others. I think it is important that I remain healthy, I really do.'