US President Barack Obama is to visit Hiroshima on Friday, where the US dropped the world's first nuclear bomb.
The visit, after the G7 summit, will be the first to the Japanese city by a serving US president.
Mr Obama has said he will not be issuing an apology for the nuclear attack, but will honour all those who died in World War Two.
He told Japanese media the visit would show that "even former adversaries can become the strongest of allies".
"Hiroshima reminds us that war, no matter the cause or countries involved, results in tremendous suffering and loss, especially for innocent civilians," he wrote in the Asahi newspaper.
The nuclear bombing of Hiroshima on 6 August 1945 killed at least 140,000 people.
Two days later a second nuclear bomb was dropped on Nagasaki, killing another 74,000.
Mr Obama will lay a wreath at the cenotaph, where an eternal flame remembers Hiroshima's dead. He will be joined by bomb survivors living in the now thriving city.
Many in the US believe the use of the nuclear bomb, though devastating, was right, because it forced Japan to surrender, bringing an end to World War Two.
The daughter of one survivor, who was visiting the memorial on Friday, said the suffering had "carried on over the generations".
"That is what I want President Obama to know," Han Jeong-soon, 58, told the Associated Press. "I want him to understand our sufferings."
The BBC's John Sudworth in Hiroshima says there is likely a strategic purpose to the visit, as a symbol of the deepening alliance between Washington and Tokyo in a region wary of China's rising military might.