Barack Obama has laid a wreath at Hiroshima in Japan, the city destroyed by an American atomic bomb in 1945.
He is the first serving US president to visit the city, where at least 140,000 people were killed.
In his address, he said: "Death fell from the sky and the world was changed."
Hideki Asari, from the Japanese Embassy, hopes the visit will make a difference: “We saw the President Obama talking very attentively to survivors and embraced one of them and it was a very moving scene to watch.
“It is very important to strive for a world free of nuclear weapons.”