President Barack Obama on Friday arrived in Hiroshima, the first visit by a sitting US president to the site of the world's first atomic bombing.
"Seventy-one years ago on a bright cloudless morning, death fell from the sky and the world was changed," Obama said at the Hiroshima Peace Memorial Park. He was being accompanied by Japanese Prime Minister Shinzo Abe.
Obama flew into the Iwakuni US base, some 40 kilometres from Hiroshima, after leaving the G7 summit.
"A flash of light and a wall of fire destroyed a city, and demonstrated that mankind possessed the means to destroy itself."
At least 140,000 people were killed in Hiroshima on August 6, 1945, in what was the world's first nuclear bombing. Two days later a second nuclear bomb was dropped on Nagasaki, killing another 74,000.
Obama's remarks expressed sadness and regret but stopped short of an apology. They came after he laid a wreath on the cenotaph bearing an inscription in Japanese: "Let all the souls here rest in peace; For we shall not repeat the evil."
"Why do we come to this place, to Hiroshima? We come to ponder the terrible force unleashed in the not so distant past. We come to mourn the dead," Obama said.
In the museum's guest book, the president wrote that he hoped the world will "find the courage, together, to spread peace, and pursue a world without nuclear weapons."
Obama's visit to the site of the devastation in August 1945 that killed over 140,000 people in one go was at least six years in the making inside the White House.
Japanese officials had initially discouraged Obama from coming, but the final ground was paved by Secretary of State John Kerry, who visited the memorial and museum in April.
Former president Jimmy Carter (1977-1981) had visited Hiroshima in May 1984, after the end of his term in office.
Obama is expected to meet some survivors of the blast, most of whom were young children at the time their city was destroyed and at least 140,000 lives were lost.
Sunao Tsuboi, a survivor, said he "never imagined (the president) would come while I am alive".
"We do not need apologies," Tsuboi added.
"I hope that he will present in Hiroshima what is good for the happiness of humankind. I would like to join hands with each other through the power of reason and beyond hatred."
