Doves fly over the Hiroshima Peace Memorial Park during thr memorial ceremony to mark the 70th anniversary of the atomic bombing of Hiroshima. [Photo/CFP]

Although he made no direct reference to the controversial security-related bills being discussed in the upper house of the Diet, he urged the world leaders to promote "the path to true peace revealed by the pacifism of the Japanese constitution."

Japanese Prime Minister Shinzo Abe attended the ceremony and delivered a speech calling for a nuclear-weapon-free world.

"Japan is the only country in the world that has suffered atomic bombing in war. It is our mission to convey to the world and to the coming generations the inhumane nature of nuclear weapons," he said.

As Abe spoke, shouts of protest rang out from the audience and around the park. "We strongly oppose the security-related bills." "Retract the war bills." shouted the protesters, holding banners.