Researchers are now convinced that the Zika virus is linked to the birth defect microcephaly, with dozens of suspected cases under investigation in Colombia, and to Guillain-Barre, a rare neurological disorder that can cause paralysis, the World Health Organization said on Thursday.

In its previous weekly report, the United Nations agency said the mosquito-borne virus that is spreading across Latin America and the Caribbean was "highly likely" to be a cause.

"Based on observational, cohort and case-control studies, there is a strong scientific consensus that Zika virus is a cause of GBS (Guillain-Barré​ Syndrome), microcephaly and other neurological disorders," the WHO said in an update.

Six countries where Zika virus is not known to be spreading by mosquitos have now reported locally acquired infection,

probably through sexual transmission, it said, naming Argentina, Chile, France, Italy, New Zealand and the United States.

The WHO declared the Zika outbreak an international health emergency on Feb. 1, citing a "strongly suspected" relationship between Zika infection in pregnancy and microcephaly.

Though Zika has not been proven to cause microcephaly in babies, there is growing evidence that suggests a link. The

condition is defined by unusually small heads that can result in developmental problems.

Microcephaly and other fetal malformations have also been reported in Colombia, where 56,477 suspected cases of Zika virus including 2,361 laboratory-confirmed have been reported.

Thirty-two babies have been reported as being born with microcephaly in Colombia this year and they remain under

investigation to establish the association with Zika virus, the WHO said, citing figures provided by the country on March 30.

Two babies from Cabo (Cape) Verde in Africa have also been reported as having microcephaly, it said.

To date, 13 countries or territories have reported increased incidence of Guillain-Barre and/or laboratory confirmation of a Zika virus infection among GBS cases, it added.