Brazil's Olympic Games should be postponed or moved to avoid intensifying the spread of the zika virus, according to a letter signed by 151 scientists.
The World Health Organization (WHO) disagreed, saying Friday that the event would "not significantly alter" the spread of the virus, which has been linked with microcephaly in babies born to affected mothers.
"WHO must revisit the question of Zika and postponing and/or moving the Games," said the scientists' open letter to the WHO director general, Margaret Chan.
The International Olympic Committee (IOC) has also said the Games' schedule will not need to be changed out of the health concerns.
"We recommend that WHO convene an independent group to advise it and the IOC in a transparent, evidence-based process in which science, public health, and the spirit of sport come first," the scientists wrote.
"Given the public health and ethical consequences, not doing so is irresponsible," the letter said, adding that half a million people are expected to travel to the Games in Rio de Janeiro.