Circumcising men can help protect them from the AIDS virus, researchers said on Tuesday after finishing the first study that tried using the procedure specifically to prevent infection.

But United Nations health officials cautioned that more trials were necessary before they would recommend this as a method to protect against AIDS. The circumcised men were 65 percent less likely to become infected with the deadly and incurable virus, the researchers told the International AIDS Society Conference in Rio de Janeiro.

Several studies have suggested that men who are circumcised have a lower rate of HIV infection. This has been especially noticeable in some parts of Africa, where some groups are routinely circumcised while neighboring groups are not.

Researchers believe circumcision helps to cut infection risk because the foreskin is covered in cells that the virus may also survive better in a warm, wet environment like that found beneath a foreskin.