ISE-SHIMA (AFP) - Barack Obama's historic visit to Hiroshima will underline the dangers of warfare and the need to work towards peace, the US president said on the sidelines of the G-7 summit in Japan, on Thursday (May 26).

"I want to once again underscore the very real risks that are out there and the sense of urgency that we all should have," he told reporters at the summit venue in Ise-Shima.

Obama, who will Friday become the only sitting US president ever to visit Hiroshima - the site of the world's first nuclear bomb - said the Aug 6, 1945 attack was "an inflection point in modern history".

"It is something that all of us have had to deal with in one way or another," he said.

The bombing claimed the lives of 140,000 people, some of whom died immediately in the ball of searing heat, while many succumbed to injuries or radiation-related illnesses in the weeks, months and years afterwards.

Obama has said he will not apologise or address the debate on whether the atomic bombing of Hiroshima and on Nagasaki three days later was justified, but will honour all those who lost their lives in World War II.

He will be accompanied by Japanese Prime Minister Shinzo Abe on the visit.

The attack is no longer as present in the modern mind as it was during the decades of the Cold War, said Obama.

"But the backdrop of a nuclear event remains something that presses on the back of our imagination."

At least three atomic bomb survivors will attend the event in Hiroshima on Friday, Japan's Kyodo news agency reported.