A Roman Catholic group appealed to Pope Francis on Wednesday to allow Church members to "follow their conscience" and use contraception or to let women have abortions to protect themselves against the Zika virus.

The appeal came as the World Health Organization (WHO) advised women in areas with the virus to protect themselves, especially during pregnancy, by covering up against mosquitoes and practising safe sex with their partners.

Zika has been linked to severe birth defects in thousands of babies in Brazil and is spreading rapidly in the Americas. The first known case of Zika in the United States was reported last week by local health officials, who said it was probably contracted through sex and not a mosquito bite.

Catholics for Choice, a liberal advocacy group based in Washington, said in a statement it would run ads in the International New York Times and El Dario de Hoy in El Salvador on Thursday, the eve of a papal trip to Cuba and Mexico.

"When you travel tomorrow (Friday) to Latin America, we ask you to make it clear to your brother bishops that good Catholics can follow their conscience and use birth control to protect themselves and their partners," the ad will say, according to advance excerpts released in the statement.

Catholics for Choice asked Francis, Latin America's first pope, to "really stand in solidarity with the poor".

"Women's decisions around pregnancy, including the decision to end a pregnancy, need to be respected, not condemned," it said.

The Catholic Church teaches that life begins at the moment of conception and that abortion is killing. It bans artificial birth control such as condoms, arguing that they block the possible transmission of life.

The ban, enshrined in Pope Paul's 1968 Encyclical "Humanae Vitae," is widely disregarded in many advanced countries, but activists say there is still a stigma attached to birth control in some Latin American countries because of the edict.

In 2010, former Pope Benedict said in a book that the use of condoms to stop the spread of AIDS may be justified in certain exceptional cases. The Vatican has so far not addressed the issue of contraception in relation to the Zika crisis.

In its announcement on Wednesday, the WHO said: "Women who wish to terminate a pregnancy due to a fear of microcephaly should have access to safe abortion services to the full extent of the law."

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