Washington ? The U.S. military is exploring ways to use drugs such as Valium to calm people without killing them during riots or other crowd control situations where lethal weapons are inappropriate.

Some critics say the effort violates international treaties and federal laws against chemical weapons, an allegation the military denies.

“It’s a rotten idea to drug rioters,” said Edward Hammond of the Sunshine Project, a chemical and biological weapons watchdog group that is the program’s chief critic. “Beyond being a horrible idea, it’s illegal.”

The Pentagon has long tried to develop nonlethal weapons that would incapacitate or repel people with little risk of killing them. The effort intensified in the 1990s after hostile mobs confronted U.S. troops during peacekeeping and humanitarian missions in places like Somalia, Bosnia and Haiti.

Officials in the military’s Joint Non-Lethal Weapons Directorate began discussing whether it would be possible to develop drugs for use as “calmatives,” or chemical peacemakers. Those discussions continued at a seminar with British military officials in 2000, according to a joint report on the meeting.

“During war game scenarios, numerous participants expressed the desire to have a NLW (non-lethal weapon) that could quickly incapacitate individuals with little or no aftereffects,” the report said.

Researchers at a Pentagon-funded institute at Pennsylvania State University prepared a 50-page report that year saying that developing calmative weapons “is achievable and desirable” and suggesting drugs like Valium for further research.

That’s as far as the military went, spokesmen for Pennsylvania State and the military said. University spokeswoman Vicki Fong said the researchers initiated the study themselves, not under a request from the military.

The chemical weapons treaty allows military and police forces to use riot control agents, such as tear gas and pepper spray, that produce temporary irritation. The treaty bans use of chemicals that incapacitate people, however.