All donated blood should undergo tests for the Zika virus, which can cause birth defects, US regulators said Friday, amid a mounting outbreak of the mosquito-borne virus in the United States.

"There is still much uncertainty regarding the nature and extent of Zika virus transmission," said Peter Marks, director of the Food and Drug Administration's Center for Biologics Evaluation and Research.

"At this time, the recommendation for testing the entire blood supply will help ensure that safe blood is available for all individuals who might need transfusion."