But men should still use condoms and other protection against the virus, said the World Health Organization and UNAIDS, the U.N. agency that coordinates the global fight against the AIDS virus.
"We must be clear," said Catherine Hankins, of UNAIDS. "Male circumcision does not provide complete protection against HIV."
Besides condoms, men and women should use protections such as abstinence, delaying the start of sexual activity and reducing the number of sexual partners, she said.
Otherwise, they could develop a false sense of security and engage in high-risk behavior that could undermine the partial protection provided by male circumcision, the agencies said.
Men also should be warned that they are at a higher risk of being infected with HIV if they resume sex before their circumcision wound has healed, which can take six weeks. Likewise, an HIV-positive man can more easily pass the disease to his partner if the wound has not unhealed.
More study is needed to determine whether male circumcision will cut the transmission of HIV to women or reduce HIV infection in homosexual intercourse, the statement said.
"It probably does, but we don't have sufficient research now to confirm that," said Dr. Teguest Guermo of WHO. "We will be doing some more research on that."
The recommendations were based on a conference in which experts discussed three trials — in Kenya, Uganda and South Africa — that produced strong evidence of the risk reduction resulting from heterosexual male circumcision.
"Based on the evidence presented, which was considered to be compelling, experts attending the consultation recommended that male circumcision now be recognized as an additional important intervention to reduce the risk of heterosexually acquired HIV infection in men," a joint statement said.
WHO experts said the trials convinced them after 20 years of observations that circumcision reduces men's susceptibility to HIV infection partly because the cells in the foreskin of the penis are especially vulnerable to the virus.
The findings tied in with lower HIV rates in North and West African countries where circumcision has been widely practiced for religious or cultural reasons.
Much depends on the situation in a given country, and little general benefit will result in countries where the HIV epidemic is concentrated among intravenous drug users or men who have sex with men, the agencies said.
The public health impact is likely to be most rapid where there is a high rate of HIV infection among men having sex with women. In those countries with low circumcision rates, health authorities should urgently consider making the procedure more widely available, the agencies said.
Studies suggest male circumcision could prevent 5.7 million new cases of HIV infection and 3 million deaths over 20 years in sub-Saharan Africa, they said.
An estimated 665 million men, or 30 percent of men in the world, are circumcised, but the rate varies considerably from country to country, it said.
The agencies said the risks involved in male circumcision are generally low, but can be serious if the operation is performed in unhygienic settings by poorly trained, ill-equipped health workers.
But with proper training, the operation can be performed safely under local anesthesia by "midlevel" health workers like nurses or clinical officers at a cost of $50 to $100 per person, WHO said.
Priority should be given to providing circumcision to age groups at highest risk of acquiring HIV because it will have the most immediate impact on the disease. But, the statement said, circumcising younger males also will have a public health impact over the long term.
Susan Timberlake of UNAIDS stressed that women should know that there is no evidence that they will be protected from HIV if they have sex with a circumcised man.