(CNN) The World Health Organization says the mosquito-borne Zika virus causes microcephaly and Guillain-Barre syndrome.
"Based on a growing body of preliminary research, there is scientific consensus that Zika virus is a cause of microcephaly and Guillain-Barre syndrome," the World Health Organization said in its weekly Zika virus situation report Thursday.
Previously, the agency said there was not yet enough scientific evidence to say the virus caused these conditions, although it was likely.
More than 1,000 cases of microcephaly and other fetal malformations believed to be Zika-associated have been reported from six countries, according to the WHO.
There have been nearly 400 cases of Guillain-Barre syndrome in patients with confirmed or suspected Zika virus infection in 13 countries.
The agency said research continues to determine a "causal link" between the Zika virus and neurological disorders in fetuses, newborns, infants and adults. This includes trying to quantify what the risk is for pregnant women and others.
Since last year the virus has infected hundreds of thousands of people in nearly 60 countries. Symptoms include a rash, fever, joint pain and red eyes (conjunctivitis). However, 80%of those infected have no symptoms. The virus is primarily transmitted via infected Aedes aegypti mosquitoes, but it is also sexually transmitted.
In February the WHO declared a public health emergency of international concern over the virus. This was prompted largely by how fast the outbreak was spreading and because of the link -- just suspected, at that time -- to microcephaly and other possible neurological defects. The agency predicts 3 to 4 million people will be infected within a year.