Speaking after a high-level meeting of flu experts and U.S. security officials in Geneva, a WHO official said an agreement had been reached in principle to keep details of the controversial work secret until deeper risk analyses have been carried out.

"There is a preference from a public health perspective for full disclosure of the information in these two studies. However there are significant public concerns surrounding this research that should first be addressed," said Keiji Fukuda, the WHO's assistant director-general for health security and environment.