The World Health Organization (WHO) has played down concerns over the spread of the Zika virus, amid calls for the Rio Olympics in August to be postponed.

The WHO's Bruce Aylward told the BBC risk assessment plans were in place. He admitted that the WHO could "do a better job" at communicating what was being done, but reiterated that there was no need to postpone the Games.

The International Olympic Committee (IOC) has said it sees no reason to delay or move the Games because of the mosquito-borne disease. Mr Aylward said that a call to postpone the Games could not be ruled out in the future, but added: "All the information available today... suggests that the games should definitely go ahead." He restated the WHO's warning that women who are pregnant or seek to get pregnant should not travel to the Zika zone or be exposed to returning partners who may have been infected.

Postponing the games, at this stage, would only "compromise the huge investment that athletes and others have made in preparing for what should be a fantastic occasion." Zika infection in pregnant women has been shown to be a cause of microcephaly and other brain abnormalities in babies.

In February, the WHO declared recent outbreaks of those diseases in Latin America and French Polynesia a global health emergency requiring a united response. It said stepping up programmes to eradicate mosquitoes that spread the Zika virus were a priority.

The letter was signed by 150 international scientists, doctors and medical ethicists from such institutions as Oxford University and Harvard and Yale universities in the United States.

They cite the failure of a mosquito-eradication programme in Brazil, and the country's "weakened" health system as reasons to postpone or move the Olympics in "the name of public health"