The U.S. Centers for Disease Control and Prevention (CDC) has confirmed that the Zika virus causes severe birth defects, including microcephaly, BBC News reports.

Hundreds of babies were born in Brazil last year with microcephaly, a syndrome where children are born with unusually small heads.

The defects coincided with a spike in Zika infections, leading experts to suspect the mosquito-borne virus. Research has now affirmed those experts' suspicions, the CDC said.

U.S. health officials warned the Zika outbreak could have more of an effect on the United States and called for additional funding to combat the virus. "Everything we know about this virus seems to be scarier than we initially thought," said Dr Anne Schuchat of the CDC.

Zika virus was first diagnosed in 1947 in Uganda, but symptoms have typically been mild, including rash, joint pain and fever.

The current outbreak started in 2015 in Brazil and the symptoms have been much more severe. Nearly 200 babies have died as result of the virus.

There have been 346 confirmed cases of Zika in the continental United States, according to the CDC, all associated with travel. The CDC has discouraged pregnant women from travelling to places where the Zika virus is spreading, mostly in Latin America and the Caribbean.