US senators called Thursday for an end to a 1983 US rule that bans gay men from donating blood, calling the prohibition "outdated, medically and scientifically unsound."

Democratic Senator John Kerry led a group of 17 Democrats and one independent in writing US Food and Drug Administration Commissioner Margaret Hamburg to urge the agency to lift the restriction.

"We write today to express our concerns regarding outdated, medically and scientifically unsound deferral criteria for prospective blood donors," they wrote in the letter, which Kerry's office made public.

"With hospitals and emergency rooms across the country in constant and urgent need of blood products, we believe certain blood donor deferral policies should be reviewed and appropriately modified and modernized while ensuring the blood supply meets the highest possible standards," they wrote.

The American Red Cross and other health organizations support ending the ban, saying the law is "medically and scientifically unwarranted."

"All donated blood is mandated to be tested for HIV with two different, highly accurate tests. Between these two tests, the risk of tainted blood entering the blood supply undetected is virtually zero," said Kerry's office.

The ban, enacted at the height of the HIV/AIDS crisis, bars men who have ever had sex with other men after 1977 from donating blood.

Kerry's office noted that prospective blood donors who have engaged in heterosexual sexual activity with a person known to have HIV are deferred for one year, while men who engage in protected gay sex are barred for life.