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.
The conclusion should settle months of debate about the connection between the infection and these birth defects, called microcephaly, as well as other neurological abnormalities, the officials said.
"This study marks a turning point in the Zika outbreak. It is now clear that the virus causes microcephaly," said Dr Tom Frieden, the head of the CDC.
Dr Frieden said that this is the first time that mosquito bites have caused birth defects. The virus can be transmitted by sexual contact as well. Intensive research was under way to find out much more about the mosquito-borne virus and to develop a vaccine for it, although he warned that could still be years away.
He and other agency officials said they hoped that the announcement increased awareness and concern about the potential threat to Americans who travel to affected areas in Latin America and those living in Puerto Rico, American Samoa and Southern states where the virus is expected to arrive this summer.
There have been 346 confirmed cases of Zika in the continental United States, according to the CDC, all associated with travel.
On Monday, US 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.
Researchers are interesting learning why some cases of the virus result in birth defects while others do not. Some women who were infected with Zika while pregnant gave birth to apparently healthy children.