The Vatican today broadened the scope of the pope's remarks about the use of condoms to prevent Aids, apparently opening the way for their widespread use by Roman Catholics in Africa and other parts of the world blighted by the disease.

The leaking at the weekend of differently translated passages of a book of interviews with Benedict XVI generated intense controversy. According to the German original and the English translation, Benedict said the use of a condom by an HIV-positive male prostitute could be a good thing, in that would represent a first step towards an assumption of responsibility; in the Italian version, however, the word for a female prostitute was used.

Several commentators, particularly conservative ones, pounced on the pope's unusual example to claim he was not signalling 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, the pope's 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, Light of the World, by German journalist Peter Seewald, cannot alter doctrine. But Father Lombardi's comments signalled that the pope approved 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 purely contraceptive purposes remains. One of the pope's most senior officials, Cardinal Rino Fisichella, told the press conference it was "intrinsically an evil".

What remains to be seen, however, is whether the Catholic church will be able to sustain a meaningful distinction between the dual uses of the condom.

Benedict's comments do not detract from his insistence that abstinence and fidelity are more important in fighting Aids. On his visit to Africa last year, he prompted criticism by suggesting the distribution of condoms could even aggravate the problem.

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 the use of condoms, he gives an answer that falls well short of a straight yes.

"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 pope's shift appeared to have caught unawares even some of his own most senior officials. Asked by the website of the US-based National Catholic Register whether Benedict's statement indicated that in some cases condoms were permissible, Cardinal Raymond Burke replied flatly: "No, it's not."

Cardinal Burke, who heads the Vatican's highest appeals court, said the pope was "simply making the comment that [if] a person who is given to prostitution at least considers using a condom to prevent giving the disease to another person – even though the effectiveness of this is very questionable – this could be a sign of someone who is having a certain moral awakening. But in no way does it mean that prostitution is morally acceptable, nor does it mean that the use of condoms is morally acceptable."