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.