Image copyright Reuters Image caption Pope Francis insisted that abortion was still considered a crime

Pope Francis has hinted that the use of contraception by women at risk of contracting the Zika virus may be permissible.

The pontiff insisted that abortion remained a crime but said avoiding pregnancy was "not an absolute evil".

His remarks came in response to a question about how best to tackle the Zika outbreak across Latin America.

The virus has been linked to the microcephaly birth defects in babies, which can cause development problems.

Roman Catholic teachings currently ban the use of contraception.

"We must not confuse the evil consisting of avoiding a pregnancy with abortion," Pope Francis told reporters on a flight returning home from a visit to Mexico.

"Abortion is not a theological problem. It is a human problem, medical. One person is killed to save another. It is evil in itself, it is not a religious evil, it is a human evil," he said.

"Avoiding a pregnancy is not an absolute evil. In certain cases, as in this one, or in the one I mentioned of Blessed Paul VI, it is clear," he went on.

The 79-year-old was referring to a predecessor's decision to authorise nuns at risk of rape in Africa to use contraceptives.

Analysis - Caroline Wyatt, Religious Affairs Correspondent

The Pope's comments about avoiding pregnancy in areas where the Zika virus is prevalent are an immensely significant moment. While he does not specifically condone artificial contraception, which is against Roman Catholic teaching, he appears to signal an unexpected openness to the idea if used in order to prevent further infection.

Asked directly whether the Church would consider it permissible to use contraceptives in order to prevent transmission of Zika, Pope Francis said that in some cases the "lesser of two evils" could be applied and spoke of example of Blessed Paul VI, a Pope in the early 1960s who allowed nuns in Africa to use birth control in order to prevent them conceiving children from rape.

That leaves the door open to Catholic families in affected areas to follow their own consciences on the matter. However, the Pope made abundantly clear that abortion remained "a crime, an absolute evil," while birth control was not an "absolute" evil.

Scientists said on Thursday that links between the Zika virus and microcephaly have been strengthened by a study involving pregnant women in Brazil.

The research confirmed the presence of Zika virus in the amniotic fluid of two women who had had Zika-like symptoms during their pregnancies.

Brazilian experts say this suggests the virus can infect the foetus. But World Health Organisation experts caution the link is not proven and expect to release more information in the next few weeks.

Image copyright AP Image caption A 10-year-old Brazilian boy holds his two-month-old brother, who was born with microcephaly

The United Nations and aid organisations have urged countries hit by the virus to ensure women have access to contraception to reduce the risk of infection and the right to abortion should they decide to terminate a pregnancy.

Many Latin American countries outlaw abortion or allow it only if the mother's life is in danger.

After initially saying little about the outbreak, Catholic leaders in the region had recently begun to assert the Church's opposition to what it terms "artificial" birth control and abortion.

Instead of using condoms or the contraceptive pill, Church officials have been recommending abstinence or what they term natural family planning - scheduling sexual relations for the least fertile periods of a woman's menstrual cycle.