Washington, D.C. ? Circumcising adult men may reduce by half their risk of getting the AIDS virus through heterosexual intercourse, the U.S. government announced Wednesday, as it shut down two studies in Africa testing the link.

The National Institutes of Health closed the studies in Kenya and Uganda early, when safety monitors took a look at initial results this week and spotted the protection. The studies’ uncircumcised men are being offered the chance to undergo the procedure.

The link between male circumcision and HIV prevention was noted as long ago as the late 1980s. The first major clinical trial, of 3,000 men in South Africa, found last year that circumcision cut the HIV risk by 60 percent.

Still, many AIDS specialists had been awaiting the NIH’s results as a final confirmation.

“Male circumcision can lower both an individual’s risk of infection, and hopefully the rate of HIV spread through the community,” said AIDS expert Dr. Anthony Fauci, director of the NIH’s National Institute of Allergy and Infectious Diseases.

But it’s not perfect protection, Fauci stressed. Men who become circumcised must not quit using condoms nor take other risks – and circumcision offers no protection from HIV acquired through anal sex or injection drug use, he noted.

“It’s not a magic bullet, but a potentially important intervention,” agreed Dr. Kevin De Cock of the World Health Organization.