Colombia has confirmed the first two cases of a rare birth defect associated with the spread of Zika.

The National Institute of Health on Thursday said that of the 33 cases of microcephaly reported so far this year, two have been confirmed to have been caused by the mosquito-borne virus. Another 15 cases remain under analysis while 16 cases have been ruled out for any relation to the virus.

The said that one case was in Norte de Santander department near the border with Venezuela and the other in the lowland areas near the capital, Bogota. No other details were provided out of respect for the families' privacy.

Zika has been related to a surge in babies born with small heads in Brazil. Despite the virus' spread across Latin America, no cases of microcephaly have been discovered elsewhere until now except for one case involving a baby in Panama

The announcement comes a day after the Centers for Disease Control confirmed that there's no doubt Zika is a cause of the birth defects.

Colombian authorities have been on the lookout for a rise in microcephaly ever since the epidemic hit Brazil. But authorities say the 33 of microcephaly reported in the country so far in 2016 don't represent a statistical aberration from previous years.