Pope Francis suggested Thursday that contraceptives may be morally acceptable to avoid spreading the Zika virus, framing their use as “not an absolute evil” compared with abortion and setting off a debate about whether the pontiff’s remarks were unprecedented.

Francis was on a plane back to Rome after a six-day trip to Mexico when a reporter asked him whether he thought abortion or avoiding pregnancy could be “the lesser of two evils” in responding to the mosquito-borne Zika virus, which has hit Latin American countries hard.

“Abortion is not the lesser of two evils. It is a crime. That’s what the Mafia does,” the pope said, according to a transcript from the Catholic News Agency.

Francis cited the decision made by Pope Paul VI in the 1960s to permit nuns in Belgian Congo to use artificial contraception to prevent pregnancies because they were being systematically raped. “On the other hand, avoiding pregnancy is not an absolute evil,’’ he said. “In certain cases, as in this one [Zika], such as the one I mentioned of Blessed Paul VI, it was clear.”

It was not immediately clear what effect the pope’s remarks would have in heavily Catholic Latin America, where cases of Zika are multiplying. Researchers increasingly believe the virus is linked to thousands of cases of microcephaly — a condition in which babies are born with small heads and brain abnormalities — in Brazil. There also is evidence that the virus is spread through sexual transmission in some ­cases.

Pope Francis gestures as he speaks to reporters aboard the papal plane en route to Rome after his six-day trip to Mexico. (Alessandro Di Meo/Reuters)

When recently asked about Catholic teaching and Zika, some prominent Catholic leaders in the region have emphasized that artificial contraception is immoral. But the issue of whether it might be acceptable in the case of Zika is “a question that’s still under debate,” said Monsignor Gregorio Rosa Chávez, auxiliary bishop of San Salvador.

Some church leaders might be waiting to make statements about the virus because the scientific link between Zika and microcephaly in infants has not been scientifically proved, said Richard Coll, foreign policy adviser for Latin America and global trade at the U.S. Conference of Catholic Bishops, who was in El Paso-Juarez at the U.S.-Mexico border for the pope’s Mass on Wednesday. Health officials warn that it may take months to know more definitively.

Contraceptives are legal and widely used in many parts of Latin America, although poor and rural areas often suffer shortages.

Theologians disagreed about whether the outspoken pontiff had said something new. Popes in the past have spoken of exceptions to the ban on artificial contraception, but the debate Thursday centered on the context.

Pope Benedict XVI made news in 2010 when he said condoms might be acceptable for a male prostitute, a comment welcomed by many activists in parts of Africa where the AIDS virus was rampant. But Benedict spoke about it as “a first step” toward improving morality.

Boston College moral theologian Cathleen Kaveny said Francis’s comments might be seen as a “development” in theology because he suggested contraception can be used to prevent pregnancy even in a consensual sexual relationship.

Also unusual: Francis’s comments were pragmatic and pastoral, Kaveny said. Previous leaders appeared more focused on policy statements aimed at changing behavior, she said.

But other experts saw Francis’s remarks as classic Catholic theology.

“It would be a bad mistake to think of this as a liberal pope changing Catholicism again,” said Charles Camosy, a moral theologian at Fordham University. Benedict “asked the same kind of questions and responded in a similarly vague and open-to-multiple-interpretations kind of way.”

In using the example of Paul VI, Francis was in keeping with church doctrine, “in the sense that contraceptives are not an end in themselves” but used “to protect one’s well-being,” said Jorge Traslosheros, a history professor and Catholic Church expert at the National Autonomous University of Mexico.

Because the question was about “avoiding pregnancy,” it wasn’t clear what kind of contraception Francis meant — and Catholics debated that point. Some suggested that he was speaking of artificial contraception, since he mentioned a case of nuns using hormones. Others thought he could have been encouraging Catholic women to abstain or use natural family planning, which are acceptable practices in church teaching.

The Catholic Church views the use of artificial contraception and abortion as intrinsically immoral. The church does not object to certain oral pharmaceuticals that are prescribed for medical purposes, but current Catholic teaching forbids the use of oral contraceptives to prevent pregnancy.

The spread of the Zika virus has accelerated debates over contraception and abortion in Latin American countries. Mexico’s health department said Tuesday that it had confirmed six pregnant women who are infected with the virus.

Church teaching has come up against the views of some public health advocates who want women to have greater access to abortion and contraception. Health officials in some Latin American countries have advised women not to get pregnant because of the potential for birth defects caused by the virus.

Earlier this month, the U.N. High Commissioner for Human Rights called on Latin American countries to repeal their policies restricting contraception and abortion rights.

If women in Catholic-heavy Latin America do get pregnant, abortion is illegal in most countries in the region, although some have exceptions in cases of rape, fetal impairment or danger to the life of the mother.

Responses of Latin American church leaders have varied somewhat on the use of contraception in response to the virus. Bishop Leonardo Ulrich Steiner, the secretary general of the National Council of Bishops of Brazil, said in an interview with the National Conference of Bishops of Brazil that contraception was not a viable solution and that church teaching has not changed. Meanwhile, Cardinal Odilo Scherer of Sao Paulo said the use of condoms was a “personal choice.”

But like Francis, the same church leaders have drawn a hard line at abortion.

The Vatican released a statement Tuesday saying that it was concerned by the call from international leaders to increase access to the procedure, calling abortion and abortifacients “an illegitimate response to this crisis.”

“Regardless of the connection to the Zika virus . . . these children deserve to be protected and cared for throughout their lives, in accordance with our obligation to safeguard all human life, healthy and disabled, with equal commitment, leaving no one behind,” Archbishop Bernardito Auza, the Vatican’s representative to the United Nations, said on Vatican Radio.

Francis has called for a less centralized church in which local bishops have greater decision-making authority, which could mean that each region could handle the virus differently, rather than wait for a directive from Rome, said Christopher Hale, ­executive director of Catholics in Alliance for the Common Good.

“How the church in the U.S. deals with this can be different from Latin America,” Hale said. “This is going to be a great test of whether Francis’s call for a more decentralized church will bear fruit.”

Pulliam Bailey reported from New York. D. Ashley Campbell in Washington, Gabriela Martinez in Mexico City, Nick Miroff in Bogota, Colombia, and Sarah Esther Maslin in San Salvador contributed to this report.