The Catholic Church has been accused of telling people in countries with high rates of HIV that condoms do not protect against the deadly virus.
Using a condom significantly reduces the risk of contracting HIV
The claims are made in a Panorama programme called Sex and the Holy City to be screened on BBC One on Sunday.
It says cardinals, bishops, priests and nuns in four continents are saying HIV can pass through tiny holes in condoms.
The World Health Organization has condemned the comments and warned the Vatican it is putting lives at risk.
The claims come just a day after a report revealed that a young person is now infected with HIV every 14 seconds.
According to the United Nations Population Fund, around 6,000 people between the ages of 15 and 24 catch the virus every day.
Half of all new infections are now in people under the age of 25 and most of these are young women living in the developing world.
Health experts around the world urge people to use condoms to protect themselves from HIV and a host of sexually transmitted infections.
However, the Catholic Church has consistently refused to back such calls. The Vatican is opposed to contraception and has advocated that people change their behaviour instead.
But according to Panorama, the Church is now telling people that condoms do not work.
In an interview, one of the Vatican's most senior cardinals Alfonso Lopez Trujillo suggested HIV could even pass through condoms.
"The Aids virus is roughly 450 times smaller than the spermatozoon. The spermatozoon can easily pass through the 'net' that is formed by the condom," he says.
The cardinal, who is president of the Vatican's Pontifical Council for the Family, suggests that governments should urge people not to use condoms.
"These margins of uncertainty...should represent an obligation on the part of the health ministries and all these campaigns to act in the same way as they do with regard to cigarettes, which they state to be a danger."
The programme includes a Catholic nun advising her HIV-infected choir master not to use condoms with his wife because "the virus can pass through".
The Archbishop of Nairobi Raphael Ndingi Nzeki told Panaroma that condoms were helping to spread the virus.
"Aids...has grown so fast because of the availability of condoms," he said.
In Kenya, one in five people are HIV positive.
Gordon Wambi, director of an Aids testing programme in Lwak, near Lake Victoria, told the programme that he could not distribute condoms because of opposition from the Catholic Church.
"Some priests have even been saying that condoms are laced with HIV/Aids," he said.
According to Panaroma, the claims about condoms are repeated by Catholics as far apart as Asia and Latin America.
Catherine Hankins, chief scientific advisor to UNAids, condemned the Church's comments.
"It is very unfortunate to have this type of misinformation being broadcast," she told BBC News Online.
"It is a concern. From a technical point of view, the statements are totally incorrect.
"Latex condoms are impermeable. They do prevent HIV transmission."
The WHO also attacked the Catholic Church's comments.
"Statements like this are quite dangerous, " a spokeswoman told BBC News Online.
"We are facing a global pandemic which has already killed more than 20 million people and currently affects around 42 million.
"There is so much evidence to show that condoms don't let sexually transmitted infections like HIV through.
"Anyone who says otherwise is just wrong."
The aid agency Christian Aid also attacked the Vatican's attitude.
"Condoms are a straightforward and effective way of preventing HIV transmission and to suggest otherwise is dangerous," said Dr Rachel Baggaley, head of its HIV unit.