Aids campaigners have welcomed a leading Catholic cardinal's acceptance of the use of condoms if one partner in a relationship is HIV positive.
Belgian Godfried Danneels said there was a moral difference between using condoms to prevent conception and using them to prevent death, quoting from the Ten Commandments to justify his position.
"When someone is HIV-positive and his partner says 'I want to have sex with you,' then he does not have to do it," the cardinal said on Dutch television on Saturday.
"But if he does, he has to use a condom. Otherwise he will commit a sin."
UNAids told BBC News Online that the cardinal's comments were "a very positive thing".
"This news, that a very senior cardinal is willing to accept the use of condoms in particular context, and that he is arguing along the lines of scripture, is very interesting," spokesman Anindya Chatterjee said in Geneva.
"We will be watching with a lot of interest what dialogue and discussion this generates among Roman Catholics."
The Vatican rejects all artificial birth control, including condoms, to the anger of many Aids campaigners who say the stand is making the spread of HIV far harder to control.
Cardinal Danneels, 70, said sex with a person infected with HIV should be avoided.
"But if it should take place, the person must use a condom in order not to disobey the commandment condemning murder, in addition to breaking the commandment which forbids adultery," he said.
He added: "Protecting oneself against sickness or death is an act of prevention. Morally, it cannot be judged on the same level as when a condom is used to reduce the number of births."
UK campaign group the Terrence Higgins trust also welcomed the cardinal's comments.
"We very much support the cardinal's view," a spokeswoman told BBC News Online.
"The preservation of life must be of higher importance than the preservation of church regulations. Abstinence is not a practical option for many people."
Cardinal Danneels is one of the senior Roman Catholics tipped as a possible successor to the Pope.