Holding a news conference Feb. 17 on his way back to Rome after a six-day visit to Cuba and Mexico, the pope was asked if the use of artificial contraceptives or abortion could be considered "a lesser evil" when the baby had a high risk of birth defects.

"Abortion is not a lesser evil -- it's a crime," Pope Francis said. It is the deliberate taking of an innocent human life. "It's an absolute evil."

"Don't confuse avoiding pregnancy with abortion," the pope said.

The concept of a "lesser evil" may apply to artificial birth control, however, he said, pointing to Blessed Paul VI's consent in the early 1960s for women religious in the then-Belgian Congo to take the pill when rape was being used as a weapon of war.

Unlike abortion, he said, "avoiding pregnancy is not an absolute evil. In certain cases, as in this one and such as the one I mentioned of Blessed Paul VI, it was clear."

At the same time, Pope Francis pleaded with doctors and scientists "to do their utmost to find vaccines against these mosquitoes that carry this disease."

Health officials have urged women to postpone their pregnancies for two years, because the Zika virus can produce microcephaly, a rare neurological condition that causes smaller heads in newborns, affecting the normal development of their brain.

In general, the Catholic Church is opposed to artificial birth control, but promotes natural family planning to space births.