Washington (AFP) - The Zika virus has been linked to birth defects in the foetuses and babies of six women in the United States who were infected while pregnant, US health officials said Thursday.

Three of the women gave birth to infants with congenital defects such as microcephaly -- an abnormally small head -- and brain damage that are linked to Zika, the US Centers for Disease Control and Prevention (CDC) said, citing figures as of June 9.

Of the other three women, one had a miscarriage, one terminated her pregnancy, and the third gave birth to an infant that was stillborn. All three cases showed instances of Zika-related birth defects.

The six women mentioned Thursday were all infected while traveling in countries where the virus is circulating.

The CDC said it will publish weekly results of women who are pregnant and infected with Zika.

A total of 234 pregnant women in the United States had tested positive for Zika as of June 9, the CDC said.

US scientists believe that a woman infected with Zika during the first trimester of her pregnancy has a one to 13 percent chance that the fetus develops microcephaly.

The mosquito-borne Zika has spread rapidly across Latin America and the Caribbean in the past months, and experts warn that the continental United States will likely see an increase in cases as summer begins in the northern hemisphere.

There is also growing evidence that Zika can be transmitted sexually.

There is no vaccine for Zika.

The virus, which usually causes only mild, flu-like symptoms, can also trigger adult-onset neurological problems such as Guillain-Barre Syndrome, which can cause paralysis and death.