Barack Obama lays a wreath in Hiroshima.

Barack Obama lays a wreath in Hiroshima.
Photograph: Shuji Kajiyama/AP

Barack Obama has become the first sitting US president to visit Hiroshima, 71 years after the Japanese city became the target of the world's first atomic bombing and ushered in a nuclear age he has vowed to bring to an end.

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In a scene many survivors of the US bombing believed they would never live to see, Obama laid flowers at a memorial to the dead before paying tribute to the people of Hiroshima and calling on humanity to learn the lessons of the past to make war less likely.

"On a bright cloudless morning death fell from the sky and the world was changed," he said, adding that mankind had shown it had the means to destroy itself.

"Why did we come to this place, to Hiroshima? We come to ponder a terrible force unleashed in the not so distant past. We come to mourn the dead," he said.

"Their souls speak to us, they ask us to look inward, take stock of who we are," he said.

"Technological progress without equivalent progress in human institutions can doom us. The scientific revolution that led to the splitting of the atom requires a moral revolution as well.

"This is why we come to this place, we stand here, in the middle of this city and force ourselves to imagine the moment the bomb fell.

"We force ourselves to feel the dread of children confused by what they see. We listen to a silent cry.

"Someday the voices will no longer be with us to bare witness, but the memory must never fade. That memory fuels our imagination. It allows us to change."

In the distance stood the burned-out shell of the atomic-bomb dome - the most potent physical symbol of Hiroshima's recovery from the ashes of war.

As expected, Obama did not offer an apology for the decision by his predecessor, Harry Truman, to unleash an atomic bomb over the city. The attack at the end of the second world war on 6 August 1945 killed an estimated 80,000 people soon after the blast. By the end of the year the death toll had reached 140,000.

After the ceremony, Obama is reportedly planning to talk to a small group of survivors, including Sunao Tsuboi, a 20-year-old student at the time of the attack who has welcomed the president's visit as an opportunity to push ahead with international disarmament efforts.

Obama had long held the desire to go to Hiroshima, despite the potential for the visit to cause controversy in the US.

While many Japanese consider the attack a war crime - while recognising the part their country's militarist leaders played in bringing it about - the consensus in the US is that the attack hastened the end of the Pacific war, saving many more American and Japanese lives.

Japan surrendered on 15 August, less than a week after the US dropped a second atomic bomb, on the western port city of Nagasaki, killing more than 70,000 people. Obama said during a visit to Japan in late 2009 that he would be honoured to go to Hiroshima and Nagasaki.

"I certainly would be honoured - it would be meaningful for me to visit those two cities in the future," he said.

Before Friday, the only western leader to have visited Hiroshima while in office was Kevin Rudd, who laid a wreath at the peace park cenotaph in 2008 when he was Australian prime minister.

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Jimmy Carter visited the atomic bomb memorial in Hiroshima in 1984, after he had left office, but no sitting US president has ever visited the city. The highest-ranking US official to visit the site is Nancy Pelosi in 2008 when she was House speaker. Ambassador Kennedy attended the 70th anniversary commemorations last year.

The White House reportedly decided to proceed with the visit after the largely positive reaction to John Kerry's tribute to the victims of the Hiroshima bombing on the sidelines of the G7 foreign ministers' meeting last month.

Ahead of the visit, Obama told US Marines and members of the Japanese military at the Iwakuni base in western Japan how it was "a testament to how even the most painful divides can be bridged. How two nations can become not just partners but the best of friends."

His trip, he said, was an "opportunity to honour the memory of all who were lost in world war two" but also had a message for today.

Barack Obama speaks to members of the US and Japanese military Iwakuni.

Barack Obama speaks to members of the US and Japanese military Iwakuni. Photograph: Carolyn Kaster/AP

"I do think that part of the reason I'm going is because 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 said.

"So it's not only a reminder of the terrible toll of world war two and the death of innocents across continents, but it's also to remind ourselves that the job is not done in reducing conflict, building institutions of peace, and reducing the prospect of nuclear war in the future."

While polls showed most Japanese welcomed Obama's gesture, other countries in the region warned against allowing the visit to reinforce a one-dimensional view of Japan's role in the second world war.

The Chinese foreign ministry said Japan should not forget the "grave suffering" it inflicted on its neighbours during the war.

"We hope Japan can take a responsible attitude toward its own people and the international community, and earnestly take history as a mirror to avoid a recurrence of the tragedy of the war," ministry spokeswoman Hua Chunying told reporters.

The state-run China Daily went much further, claiming the "atomic bombings of Hiroshima and Nagasaki were of Japan's own making".

In an editorial on the eve of the visit, the paper accused Japan of "trying to portray Japan as the victim of world war two rather than one of its major perpetrators".

The bombing of both Hiroshima and Nagasaki was justified, the China Daily said, as "a bid to bring an early end to the war and prevent protracted warfare from claiming even more lives".

It added: "It was the war of aggression the Japanese militarist government launched against its neighbours and its refusal to accept its failure that had led to US dropping the atomic bombs."