The nuclear bombs dropped by the United States on Japan in 1945 were the inevitable way to end World War II, Japan's defence minister has said.
Hiroshima has preserved some of its ruins from the blast
"I think it was something that couldn't be helped," said Fumio Kyuma in a speech at a university east of Tokyo.
His comments sparked outrage from survivors of the bombs dropped on Hiroshima and Nagasaki.
The minister, who represents Nagasaki in parliament, said later that he was expressing the US view of events.
In his speech, he said the US must have thought the bombs "could prompt Japan's surrender, thus preventing the Soviet Union from declaring war against Japan".
Japanese leaders rarely comment on the use of the atom bomb against Japan for fear of damaging ties with the US.
Prime Minister Shinzo Abe played down Mr Kyuma's speech, saying it bore no effect on "Japan's important role of seeking abolition of nuclear weapons".
But Nagasaki survivor Terumi Tanaka, 75, said Mr Kyuma's comments were "outrageous".
"He must know hundreds of thousands of people died, and died in terrible agony," she was quoted as saying by AFP news agency.
"He is from Nagasaki, and I'm ashamed of him as a person from the same prefecture."
The row comes ahead of upper house elections on 29 July in which Mr Abe's party is facing dwindling public support.
THE ATTACK ON HIROSHIMA
0812 local time, 6 August 1945:
1. American B-29 bomber 'Enola Gay' approaches Hiroshima at an altitude of about 9,357 metres, and begins its bombing run
2. At 0815 it releases the atomic bomb 'Little Boy'
3. The aircraft then performs a sharp, 155 degree right turn and dives an estimated 518 metres
4. At 0816, the bomb explodes with a force of 13 kilotons at a height of approximately 576 metres above the city
5. About a minute later the first shock wave, travelling at about 335 metres per second, hits the aircraft