Japan has pledged to seek to eliminate nuclear weapons at a ceremony in Hiroshima to mark the 68th anniversary of the atomic bombing of the city during World War Two.
50,000 people stood for a minute's silence in Hiroshima's peace park near the site of the early morning blast on 6 August 1945 that killed up to 140,000 people.
The bombing of Nagasaki three days later killed tens of thousands more, prompting Japan's surrender to the Allies.
Prime Minister Shinzo Abe, among many dignitaries attending the event, said that as the sole country to face nuclear attack, Japan has the duty to seek to wipe out nuclear weapons.
The anniversary comes as Japan is torn over restarting nuclear power plants shut down since the massive earthquake and tsunami in 2011 damaged reactors at a plant in Fukushima, causing meltdowns.
More than 100,000 people remain displaced because of radioactivity near the plant.
Mr Abe favours restarting plants under new safety guidelines, while many Japanese oppose such restarts.
In a "peace declaration" speech, Hiroshima's Mayor Kazumi Matsui described the pain of those who survived, only to be shunned as contaminated by the radiation.
A recent agreement on discussing nuclear energy cooperation with India, he said, would likely hinder efforts to abolish nuclear weapons.
The Hiroshima victims offered their support to those suffering from the accident in Fukushima, where the situation remains precarious following meltdowns of three reactors after the plant's power systems were crippled by the tsunami.