There are now signs of a Zika outbreak in the United States.
The World Health Organization said on Tuesday it had identified 21 cases of microcephaly in the U.S. alone, including two deaths.
The virus has caused a rash of deaths, including one in Texas, where the virus is first identified in a small number of pregnant women.
The Zika virus, which is transmitted by mosquitoes, has caused severe birth defects and a rise in birth defects in the developing world, including in Brazil, where one in five women are infected.
The WHO said it would be releasing a detailed analysis of the first cases on Wednesday, and the organization said it is working with local authorities to collect the necessary information.
The Associated Press contributed to this report.