The anniversary of the world's first atomic bombing comes as regional powers continue talks in Beijing to urge North Korea to give up its nuclear programme, seen by Tokyo as a potential threat and one of the reasons behind rising calls in Japan to strengthen its defence and seek closer military cooperation with the United States.
Under a blazing summer sun on Saturday, survivors and families of victims assembled at the Peace Memorial Park near "ground zero", the spot where the bomb detonated on the morning of 6 August, 1945, killing thousands and levelling the city.
Dignitaries including Prime Minister Junichiro Koizumi attended the ceremony in Hiroshima, 690km southwest of Tokyo.
At 8.15am, the time when the US B-29 warplane Enola Gay dropped the bomb, people at the park and throughout the city observed a minute's silence in memory of those who perished.
Around 140,000 people were
killed in the blast
Bells at temples and churches rang and passengers on the streetcars that run throughout the city bowed their heads in remembrance of the dead, including those incinerated by the bomb 60 years ago while riding the streetcars.
"This 6 August ... is a time of inheritance, of awakening, and of commitment, in which we inherit the commitment of the bomb victims to the abolition of nuclear weapons and realisation of genuine world peace," Hiroshima Mayor Tadatoshi Akiba told the gathering.
Jeopardising human survival
Akiba said in his Peace Declaration that the five established nuclear powers - the United States, Russia, Britain, France and China - as well as India, Pakistan and North Korea were "jeopardising human survival".
The Hiroshima bomb unleashed a mix of shockwaves, heat rays and radiation that killed thousands instantly. By the end of 1945 the toll rose to some 140,000 out of an estimated population of 350,000. Thousands more succumbed to illness and injuries later.
Survivors worry that the reality
of the bombing will be forgotten
On 9 August 1945, three days after the Hiroshima attack, another atomic bomb was dropped on Nagasaki.
Japan surrendered on 15 August, bringing to an end the military aggression that had culminated in its entry into the second world war.
At Saturday's ceremony another 5375 names were added to the list of Hiroshima's dead, bringing the total to 242,437.
Referring to moves to revise the pacifist constitution that Japan adopted after the war, Akiba said it was an obligation of the present generation to uphold the principle "thou shalt not kill".
"The Japanese constitution, which embodies this axiom forever as the sovereign will of a nation, should be a guiding light for the world in the 21st century," he said.
There are moves to change
Japan's pacifist constitution
Earlier this week, Japan's ruling Liberal Democratic Party released a draft containing a drastic change to the constitution, proposing that the military be allowed to act not only in self-defence but also to take part in global security efforts.
Although support for revising the core pacifist clause remains short of a majority, public opinion is no longer overwhelmingly opposed to it and some politicians even talk of Japan having nuclear weapons, long a taboo.
Even some of those in Hiroshima for the anniversary said Japan may have to go nuclear to counter the North Korean threat.
"The best is if talks with the United States go well and North Korea gives up its weapons," said Yoshiaki Onoue, 45, referring to the six-party talks in Beijing aimed at persuading the North to abandon its nuclear programme.
"But Japan may need to have nuclear weapons as insurance," said Onoue, visiting the Peace Memorial Park with his family from Osaka, 300km east of Hiroshima.
Survivors, whose average age is now over 73, worry that as many of them pass away, so will memories of the bombing.
"Passing on the experience is our greatest concern," said Sunao Tsuboi, an 80-year-old survivor of the bombing who heads a group of victims.
"As we get old, even among victims the anger, that raging feeling towards the A-bomb, has waned ... 6 August is being played up this year as it's the 60th anniversary, but I wonder about next year."