150 international doctors, scientists and researchers has signed an open letter which urged the upcoming Olympic Games in Rio de Janeiro to be moved or delayed due to the Zika virus.

The letter argued that "Our greater concern is for global health. The Brazilian strain of Zika virus harms health in ways that science has not observed before".

"An unnecessary risk is posed when 500,000 foreign tourists from all countries attend the Games, potentially acquire that strain, and return home to places where it can become endemic," it said.

"Should that happen to poor, as-yet unaffected places (e.g., most of South Asia and Africa) the suffering can be great," the letter added.

Zika virus can cause birth defects and a devastating syndrome known as microcephaly in which babies are born with unusually small heads and brains.

The mosquito-borne Zika began circulating in Brazil last year due to which nearly 1,300 babies have been born in Brazil with the irreversible defect.

The Olympics and Paralympics, set for August 5 through September 18, "will take place during Brazil's wintertime when there are fewer active mosquitoes and the risk of being bitten is lower," WHO said earlier this month.