The Pentagon has introduced mandatory training on the new rules for personnel at all levels and restrictions on investigations of anyone suspected of being gay.

Since 1994, homosexuals can serve in the American armed forces as long as they don't discuss their sexual orientation.

Gay and civil rights groups say that after the adoption of the so-called don't ask, don't tell policy, attacks against homosexuals have increased and complaints often lead to prosecution.

"I've made clear that there is no room for harassment or threats in the military," Defence Secretary William Cohen said in a statement.

Baseball bat beating

Prompted by an internal report released last year and under pressure following the death last month of a gay soldier beaten with a baseball bat at Fort Campbell, Kentucky, the Pentagon reissued its original guidelines with two key changes:

• Legal and other officers at bases will now be required to consult with more senior legal officers in the military system before they pursue investigations of suspected gays.

• Formal sensitivity training aimed at curbing harassment of suspected gays will be mandatory for all US troops from boot camp onwards.

"I have instructed the military services to make sure that the policy is clearly understood and clearly enforced," Mr Cohen said.

Gay rights groups say that troops who complain of harassment are too often themselves investigated, instead of those who are the source of the harassment.