LONDON -- The World Health Organization's chief says she will convene an expert committee to consider whether the Rio de Janeiro Summer Olympics should proceed as planned, following concerns raised about the threat of the Zika virus.

In a request last month, U.S. Sen. Jeanne Shaheen asked WHO Director-General Dr. Margaret Chan to evaluate whether the Rio Games this year should be delayed or postponed. Chan said in a letter released by Shaheen on Friday that WHO has sent senior scientists to Brazil four times to assess the risk of Zika to the approximately 500,000 athletes and visitors expected to attend the Aug. 5-21 games in Brazil.

Brazil has been the hardest-hit of the approximately 60 nations that have reported Zika outbreaks - and has by far the most cases of brain-damaged babies linked to the virus, almost 1,500.

"Given the current level of international concern, I have decided to ask members of the Zika Emergency Committee to examine the risks of holding the Olympic Summer Games as currently scheduled," Chan wrote.

WHO said the meeting date would likely be fixed next week.

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Chan said she "deeply appreciated" the concerns raised by Shaheen in her letter to WHO last month, which cited a commentary by Canadian professor Amir Attaran. He argued that holding the Olympics as planned would result in the avoidable birth of more brain-damaged babies.

Last month, Attaran and more than 200 other experts signed an open letter asking WHO to convene an independent group to consider if the games should be delayed or moved "in the name of public health." WHO rejected such calls and said "cancelling or changing the location of the 2016 Olympics (would) not significantly alter the international spread of Zika."

Most people infected by Zika suffer only minor symptoms including fever, a rash and muscle or joint pain. But the virus can also cause severe birth defects, including babies born with abnormally small heads, or a rare syndrome that can cause death or temporary paralysis.

WHO declared the Zika epidemic to be a global emergency in February and in its latest assessment this week said it "does not see an overall decline in the outbreak."

WHO has already advised pregnant women not to go to Rio and says other travelers should avoid poor and overcrowded parts of the city. The U.N. agency also predicted the Zika risk in August would drop since it will be the South American winter and there should be fewer mosquitoes to transmit the virus.

Critics say WHO has an overly close relationship with the International Olympic Committee so it can't provide objective advice on Olympic issues.

IOC president Thomas Bach, however, refuted claims the organization had pressured WHO to shirk its public health responsibilities.

"There is no pressure whatsoever," Bach said Friday in Lausanne, Switzerland. "We are grateful for the cooperation with the WHO, which is giving us the information, which is helping us with data, which is helping everybody by giving advice on travel."