The World Health Organisation (WHO) has advised pregnant women not to travel to areas with continuing outbreaks of Zika virus due to the potential risk of birth defects.
It said sexual transmission was "relatively common" and health services in Zika-affected areas should be ready for potential increases in cases of neurological syndromes such as microcephaly and congenital malformations.
"Pregnant women whose sexual partners live in or travel to areas with Zika virus outbreaks should ensure safe sexual practices or abstain from sex for the duration of their pregnancy," the WHO said, based on advice from its Emergency Committee of independent experts.
Previously the UN agency had advised pregnant women to consider deferring non-essential travel to areas with ongoing transmission of the mosquito-borne virus, which is spreading through Latin America, including Olympics host Brazil.
It said the link between Zika and microcephaly, where babies were born with small heads and developmental problems, as well as Guillain-Barre syndrome, which could cause paralysis, had not been proved but studies pointed in that direction.
"Microcephaly is now only one of several documented birth abnormalities associated with Zika during pregnancy," WHO director-general Margaret Chan told a news conference. "Grave outcomes include fetal death, placental insufficiency, fetal growth retardation and injury to the central nervous system.
"It is important we recommend strong public health measures and not wait until we have definitive proof," she said.
Brazil said it had confirmed more than 580 cases of microcephaly and considered most of them to be related to Zika infections in the mothers. Brazil is investigating an additional 4100 suspected cases of microcephaly.
The WHO said airports should be sprayed to eliminate mosquitoes and their breeding grounds and authorities should consider "disinfection of aircraft".
"We can expect more cases and further geographical spread," Chan said. "Reports and investigations from several countries strongly suggest that sexual transmission is more common than previously assumed."
Bruce Aylward, WHO Executive Director for Outbreaks and Emergencies, told reporters that sexual transmission had only been documented as spreading from men to women.
"There's no evidence of women-to-men (transmission), so this dead-ends," he said.
