The Vatican today paved the way for the widespread use of condoms by Catholics, stirring impassioned theological debate among his millions of followers across the world.

In an attempt to clarify the confusion caused at the weekend by the leaking of differently translated passages from a book of interviews with the pontiff, his spokesman used its launch to signal that condom use is acceptable as a lesser evil where there was risk of HIV contagion.

Across Africa reaction to the statement exposed the divergence of views within the Catholic church. The pope's amplified comments may have created a doctrinal dilemma for hardliners.

Matthew Ndagosa, archbishop for the Kaduna diocese in Nigeria, where Catholicism is thriving, said: "Everybody is misinterpreting the Vatican. People have made up their own minds on this issue and are twisting the words to fit them.

"Holy father's message was clear – there is no change in policy. The church will continue to believe that the indiscriminate use of condoms encourages promiscuity and aggravates the situation."

But Boniface Lele, archbishop for the diocese of Mombasa in Kenya, where 30% of the population is Catholic, said he was pleased: He has been advocating change in church policy on condoms, to the displeasure of the Vatican. "In my diocese, I tell couples that if one or both or them are sick, they should use condoms. For prevention it is good thing."

Gabriel Dolan, an Irish priest who works among the poor in Mombasa, described the church's historic stance on condom use as "an injustice to those in danger" in countries which have a serious Aids problem. "This news is a relief," he said. "I think it's just the beginning. Once you make a small concession like this it's like taking a brick out of the Berlin Wall."

According to the German original and the English translation of the book, Light of the World by journalist Peter Seewald, the pontiff said the use of a condom by an HIV-positive male prostitute could be a good thing, in that it would represent a first step towards an assumption of responsibility. But in the Italian version, the word for a female prostitute was used.

Several, particularly conservative, commentators pounced on the pope's unusual example to claim he was not authorising a change in his church's opposition to artificial contraception. By referring in the original to homosexual sex, in which condoms are not used for contraceptive purposes, it was argued, he was maintaining the ban on their use in heterosexual relations.

But at a press conference in the Vatican to mark the launch of the book, his spokesman, Father Federico Lombardi, explained that he had raised this issue with the pope on Sunday.

"I personally asked the pope if there was a serious, important problem in the choice of the masculine over the feminine," Lombardi said. "He told me 'no'."

Lombardi said the key point was: "It's the first step of taking responsibility, of taking into consideration the risk of the life of another with whom you have a relationship … This is if you're a woman, a man, or a transsexual."

As several experts have noted, the book cannot alter doctrine. But Lombardi's comments show that the pope approves of condom use as a lesser evil where there was a risk of HIV contagion.

The Catholic ban on the use of condoms, or any other device, for contraceptive purposes remains. One of the pope's most senior officials, Cardinal Rino Fisichella, told the press conference condoms were "intrinsically an evil".

The pope's comments do not detract from his insistence that abstinence and fidelity are more important in fighting Aids.

In Seewald's book, he repeats his view that condoms are "not really the way to deal with the evil of HIV infection". But, asked whether his church is opposed in principle to their use, he gives a reply that falls well short of a straight answer.

"It of course does not regard it as a real or moral solution, but, in this or that case, there can be nonetheless, in the intention of reducing the risk of infection, a first step in a movement toward a different way, a more human way, of living sexuality."

The shift appeared to have caught out some of his most senior officials. Asked by the website of the US-based National Catholic Register if the pope's statement was indicating that in some cases condoms were permissible, Cardinal Raymond Burke replied flatly: "No, it's not."

Elena Curti, deputy editor of the Catholic weekly, The Tablet, welcomed the shift, saying: "[The pope] has let the genie out of the bottle. Once you do that it's very difficult to put it back in. In allowing this chink of light in – despite the careful language he uses – it does open up the debate."

The HIV charity the Terrence Higgins Trust was delighted by the announcement. "It does represent a huge shift in terms of what the Vatican said before," said the trust's communications director, Genevieve Edwards. "His comments are sufficiently broad to allow people to interpret them as they feel they need to."

But John Smeaton, a Catholic and director of the Society for the Protection of the Unborn Child, denied that there had been any policy change. "Pope Benedict, like other Catholics, is bound by the magisterium of the church which he proclaims in Caritas in veritate," he wrote on his blog. "He's not likely to promote a change to that teaching in an interview with a journalist a year later – and he doesn't do so."

The popular Catholic blogger, Father Tim Finigan, acknowledged that there had been a shift, but warned: "I must offer a reaction of my own to the holy father's comments on Aids and condoms. It would be along the lines of Sergeant Wilson in Dad's Army: 'Do you think that's wise, sir?' We know that the widespread distribution of condoms to tackle the problem of HIV/Aids has not worked in practice."