The World Health Organization has condemned any policy that allows coronavirus to spread unrestricted, warning such a move would be "epidemiological stupidity”.
However, a senior figure at the group said he did not believe Boris Johnson was actively pursuing such a policy in the UK.
The WHO's Dr Mike Ryan criticised the idea of letting coronavirus proliferate unchecked after a BBC journalist suggested the UK government had decided to do this by choosing to open up society on 19 July and lift nearly all legal restrictions related to the virus.
The journalist said the government felt it would be better to have an exit wave of cases in August, rather than September, and it was “gambling on cases going up sharply and then falling back down pretty sharply.”
Dr Ryan, WHO’s emergencies programme head, replied: “I’m not aware that’s the logic driving our colleagues in the UK, I suspect it’s not. I would like to verify that’s the logic.
“The logic of 'more people being infected is better', is logic that has proven its moral emptiness and its epidemiological stupidity”.
Watch: WHO warns of 'premature rush' back to normailty
The comments come as Johnson faces criticism for planning to ditch all social-distancing restrictions on 19 July.
Labour leader Sir Keir Starmer said the Prime Minister’s “reckless” plan would lead to a “summer of chaos and confusion”.
He warned it was “entirely predictable” people will delete the NHS COVID-19 app to avoid being told to self-isolate as cases rise.
Sir Keir has also backed keeping face masks mandatory on public transport.
Johnson has insisted that he supports mask coverings on transport, despite making them voluntary. He said “Of course we can see that it’s common sense for people in confined spaces to wear a face mask out of respect and courtesy to others, such as on the Tube.
“But what we’re doing is cautiously, prudently moving from legal diktat to allowing people to take personal responsibility for their actions – and that is the right way forward.”
In April, Johnson was accused of telling aides in the autumn of last year that he would have preferred to let COVID “rip” than impose a second lockdown.
Dr Ryan also urged countries to use extreme caution when lifting COVID-19 restrictions so as "not to lose the gains you've made".
He said that while every nation must decide for itself, individuals - including the unvaccinated - must take responsibility for protecting themselves and others and keeping hospitals from being overwhelmed by another pandemic wave.
"The idea that everyone is protected, and it's 'Kumbaya' and everything goes back to normal, I think right now is a very dangerous assumption anywhere in the world, and it's still a dangerous assumption in the European environment," he told reporters from Geneva.
"We would ask governments at this moment not to lose the gains you've made."
He said he believed British scientists were "very aware of the threat represented by variants, especially the Delta variant" and would open cautiously.
The WHO’s Dr Tedros Adhanom Ghebreyesus added the world was "at a perilous point in this pandemic" as he announced the milestone of four million recorded COVID-19 deaths had been passed.
He said: "Some countries with high vaccination coverage are now planning to rollout booster shots in the coming months and are dropping public health social measures and relaxing as though the COVID-19 pandemic is already over.
"However, compounded by fast-moving variants and shocking inequity in vaccination, far too many countries in every region of the world are seeing sharp spikes in #COVID19 cases and hospitalisation.”
Dr Tedros said vaccine nationalism, where a handful of nations have taken the lion’s share, was morally indefensible and ineffective.
The WHO urged countries, including the United States and Switzerland, which are vaccinating 12- to 15-year-old children to instead donate doses to the vaccine sharing programme COVAX.
Watch: What you need to know about COVID-19 variants