One of the authors of a letter calling for the Rio Games to be postponed over the Zika virus has said it risks becoming the "Olympics of brain damage".
Professor Amir Attaran is one of 152 health experts who have signed the letter calling for the World Health Organisation (WHO) and International Olympic Committee (IOC) to halt the event or move it elsewhere.
But the WHO has rejected the call, saying suspending or moving it would "not significantly alter" the spread of the virus.
The letter says Zika has more serious medical consequences than first thought and claims the health emergency contains "many uncertainties".
It also calls into question the relationship between the UN health agency and the IOC, which entered an official partnership in 2010.
Some 500,000 foreign tourists are expected to travel to Rio, which would lead to the virus being spread to countries it may not have reached, the letter warns.
Attaran said he believes allowing the Olympics to go ahead would lead to the birth of more brain damaged children.
He also said the partnership between the WHO and the IOC was "beyond the pale" and calls the independence of the WHO into question.
He said: "It is ignorant and arrogant for the WHO to march hand-in-hand with the IOC.
"How can it be ethical to increase the risk of spreading the virus? Just because a fire has begun doesn't mean you need to pour gasoline on it."
But a WHO statement said staging the Games would not have a major impact on the spread of the virus.
It said: "Based on current assessment, cancelling or changing the location of the 2016 Olympics will not significantly alter the international spread of Zika virus.
"Brazil is one of almost 60 countries and territories which to-date report continuing transmission of Zika by mosquitoes.
"People continue to travel between these countries and territories for a variety of reasons.
"The best way to reduce risk of disease is to follow public health travel advice."
Zika has been linked to serious birth defects including microcephaly - where babies are born with abnormally small heads and underdeveloped brains.
It has also been linked to Guillain-Barre syndrome and Acute Disseminated Encephalomyelitis which affect the nervous system.
Nearly 1,300 babies have been born in Brazil with microcephaly since the mosquito-borne Zika began circulating there last year.
The majority of those infected with the virus have no symptoms, but it can cause a mild illness with symptoms including rashes, fever and headaches.
Pregnant women have already been advised not to travel to Rio, but the WHO has said the risk of Zika will lessen in August because it is winter in Brazil.
No Olympic Games has been moved because of health concerns. But in 2003, FIFA moved the Women's World Cup from China because of fears about the respiratory virus Sars.
The Rio games are set to begin on 5 August.