Brazil's Health Ministry on Wednesday said that "most" of the 508 confirmed cases of microcephaly reported in the country are likely related to the ongoing outbreak of Zika virus infections.

The ministry earlier in the day reported a total of 4,443 suspected and confirmed cases of the rare defect, up from 4,314 a week earlier. It did not, however, update its total of 41 cases in which it said that microcephaly had been linked by laboratory tests to Zika infections.

In a clarification, it said that the government would cease to update the confirmed number of linked cases because "the Health Ministry considers that there were Zika virus infections in most of the mothers whose babies have been diagnosed" with the condition.

Of the total reported on Wednesday, Brazil said 508 cases of microcephaly have been confirmed, while 3,935 are still being investigated.

Microcephaly is a condition marked by abnormally small head size that can result in developmental problems. Brazil is investigating a surge in the number of cases across the country in conjunction with the outbreak of Zika, but have not yet proven that the virus can cause microcephaly.

Zika has now spread to more than 30 countries and has led the World Health Organization to declare a global health emergency.