A combative Pope Benedict XVI opened his trip to Brazil yesterday in no-holds-barred mood, vowing to stem the defections of Roman Catholics to evangelical Protestantism and giving a warning that the penalty for supporting abortion was excommunication.

In uncompromising remarks on “core teachings” on board the papal plane from Rome, the Pope backed the Church hierarchy in Mexico for excommunicating politicians who voted for a law that legalised abortion in the first 12 weeks of pregnancy in Mexico City, as well as doctors and nurses who performed abortions.

“This is nothing new, it is normal, it wasn’t arbitrary,” he told reporters. “It is what is foreseen by the Church’s doctrine.” He had reiterated previously the Vatican’s opposition to abortion but had not specifically backed the excommunications.

The Pope also spoke strongly against abortion during his first speech in Brazil. Speaking in Portuguese, he said he was certain that the bishops will reinforce “the promotion of respect for life from the moment of conception until natural death” as an integral requirement of human nature.

“All Latin America safeguards values that are radically Christian,” he said at a welcoming ceremony at São Paulo’s airport, flanked by Brazil’s President Luiz Inacio Lula da Silva

The issue of abortion is sensitive in Brazil, Latin America’s biggest Catholic nation, which is considering a referendum on legalising abortion.

The Pope observed that “canon law says the killing of an innocent child is incompatible with receiving Communion, which is receiving the body of Christ . . . It expresses our belief that human individuality, the human personality, is present from the first moment of life.”

Some had expected the Pope to adopt a diplomatic approach on his first significant overseas trip. A recent survey in Brazil said that 86 per cent favoured the use of condoms and more than half disagreed with the Church’s stand on abortion.

Instead, he came out with all guns blazing, a reflection of his belief that an assertion of bedrock Christian values is the only way to stem the tide toward secularism.

He said that legislators who voted in favour of abortion clearly had “doubts about the value of life and the beauty of life, even doubts about the future. Selfishness and fear are at the root of pro-abortion legislation. We in the Church have a great struggle to defend life. Life is beautiful, it is always a gift, even when lived in the most difficult circumstances.”

The Vatican has previously sidestepped the question of whether politicians who supported abortion should be banned from taking Communion. It declined to intervene in the case of John Kerry, the Democratic candidate in the US presidential election three years ago, who backed a woman’s right to abortion even though he is a Catholic.

In Latin America only Cuba, Guyana and Puerto Rico allow abortion on demand, although some countries — including Brazil — allow it if the mother’s life is at risk.

The Pope admitted that the rise of evangelical Protestant churches in Latin America was “our biggest worry”. The phenomenon showed that there was a “thirst for God” in the region, he said, but he would urge Latin America’s bishops, when he opens their conference at Aparecida, to be “more dynamic” in defending the Catholic faith.

He was equally forthright on liberation theology, the left-wing philosophy that he opposed sternly as cardinal, when he was in charge of Church doctrine. He said that he was committed to social justice, but that those who followed liberation theology were “mistakenly mixing faith and politics”. Church teaching was “not aimed at destroying the commitment to justice but guiding it along the right path”.

A spokesman for President da Silva said that the Brazilian leader would seek to avoid controversy during talks in São Paolo both over abortion and the Government’s free distribution of condoms to combat Aids.

The trip will test the 80-year-old Pope’s stamina and show whether a pontiff noted more for his scholarship than his charisma can inspire the faithful. Tight security under “Operation Archangel” has marshalled about 10,000 military, police and civilians under army command to protect the Pope on his journeys, which are to include helicopter hops and brief outings in the Popemobile.

During the trip, which ends on Monday, he will celebrate several open-air Masses, canonise Brazil’s first native-born saint and visit a Church-run drug and alcohol rehabilitation centre.