For years, Steven Leeper took the view of many fellow Americans about the nuclear bombing of Hiroshima -- that it was an inevitable part of war.

But after a lifetime of reflection, he is now the first foreigner to head an anti-nuclear foundation in the western Japanese city -- and has set his sights on persuading his country to agree with him.

"When I first came here, I completely did not think about or worry about or care about the atomic bombing," Leeper, 60, told AFP in an interview.

"In war, you just kill your enemy. And the atomic bomb is a big bomb and kills a lot of the enemy. So what's wrong with that?"

On the morning of August 6, 1945, a US bomb instantly killed more than 140,000 people in Hiroshima and injured tens of thousands of others who died later from radiation or horrific burns.

The world's first nuclear attack was followed by the dropping of a second atomic bomb on the city of Nagasaki three days later, leaving another 70,000 people dead. Japan surrendered on August 15, ending World War II.

After reading the Japanese book "Children of Hiroshima," which describes the sufferings of the atomic bomb victims, Leeper's attitude dramatically changed.

Reading the book "really caused me to suddenly think about the impact of the bomb on the society that received it," he recalled.

"Now I completely consider the atomic bombings to be a war crime," he said.

But Leeper nevertheless did not immediately join the circle of peace activists. He instead worked until last year with his wife as a consultant for Japanese firms expanding abroad to work with Hiroshima-based Mazda Motor Corp.

He said he knew he had to take action in 1998 when India and Pakistan tested nuclear weapons, declaring themselves atomic states and sending shockwaves among bomb survivors in Hiroshima and Nagasaki.

In 2007, the Hiroshima mayor appointed Leeper as the first non-Japanese head of the Hiroshima Peace Culture Foundation, which administers a museum that explains the horror of the atomic bombing.

He has been working on a project that is bringing an exhibition on the atomic bomb to the United States, with an aim of taking it to 101 cities across all 50 states.

Leeper said the exhibition has had a mixed reaction in his homeland.

"Those Americans who are 70 years or older, the ones who really hated Japan during World War II, still have ambivalent feeings about Japan, and they don't like to hear people talking about how Japan is a victim," he said.

"But young people completely have no such prejudice." After visiting US audiences with an atomic bomb survivor, "most of them are pretty shocked, many of them even have tears in their eyes sometimes," he said.

"And many of them come up afterwards, many of them actually apologised to her on behalf of America and many of them asked what they can do," he said.

But Leeper said his strategy was not to dwell on apologies over the past.

"I said from the beginning, we are not here to talk about the past. We are not here to complain, we are not accusing America of anything.

"All we are doing is warning you about the future. That's why we are here, I say."

He hoped that the issue of abolishing nuclear weapons -- not just stopping proliferation -- would get more attention in the US presidential race.

"The nuclear weapon is not just another weapon. This will kill us all absolutely, and we have to learn to control it and we have to learn to control our violence in general. And that is the key message from here," he said.

Looking ahead, he is lobbying to establish an international treaty -- the Hiroshima-Nagasaki Protocol -- that would ban all nuclear weapons around the world.

While the plan is certainly ambitious, he draws inspiration from the Kyoto Protocol, the first-ever international treaty that legally restricted carbon emissions blamed for global warming.

Leeper said that Hiroshima and other cities were collecting signatures in hopes of submitting the protocol to a UN panel by October 2009 to start negotiations.

"Just like what everybody knows about the Kyoto Protocol -- we have the general idea that it's good for the environment -- we want everybody to know that the Hiroshima-Nagasaki Protocol shows a commitment to a nuclear-free world," he said.