that nuclear weapons are extremely dangerous and should never be used," said Leeper, a 59-year-old Illinois native, at the Japan National Press Club in Tokyo. "We want them to make sure that they communicate that to their leaders."

Leeper is particularly alarmed by the U.S. for its flirtation with mini-nukes and its decision last year to give India civilian nuclear knowhow and access to nuclear fuel even though it is not a signatory to the Nuclear Nonproliferation Treaty. Instability in other regions could also spark chaos, said Leeper.

"Right now we face the serious possibility that the United States could use a nuclear weapon in Iran," he said.