The head of international anti-nuclear group ICAN said Monday that Japanese leadership should not fear the U.S. government's reaction and move to recognize the Treaty on the Prohibition of Nuclear Weapons as the ban marks its third anniversary.

"It's silly to be frightened of the risk coming from what the Americans think about observing or joining the treaty," Melissa Parke, executive director of the International Campaign to Abolish Nuclear Weapons, said in an interview.

"When you compare that to the risk of nuclear weapons, I think it's important to have some perspective," the former Australian lawmaker said amid her first Japan visit since becoming ICAN's head in September. She also went to Hiroshima and Nagasaki and met hibakusha atomic bomb survivors, among others.