The mayor of Hiroshima rebuked Washington on Friday - the 59th anniversary of his city's atomic bombing by the United States - for wanting to develop small nuclear weapons that he feared would be easier to use.
Hiroshima Mayor Tadatoshi Akiba made the remarks at a ceremony attended by about 40,000 people, including Japanese Prime Minister Junichiro Koizumi plus survivors and relatives of victims of the world's first atomic attack.
"The egocentric world view of the US government is reaching extremes," Akiba told the annual memorial ceremony at the city's Peace Park, near where the bomb was dropped.
"Ignoring the United Nations and its foundation of international law, the US has resumed research to make nuclear weapons smaller and more 'usable'."
The Peace Bell was tolled at 8:15 am - the moment a US warplane dropped the bomb on August 6, 1945 and destroyed the city - and there was a minute of silence.
The names of 5,142 people who died recently were added to the list of victims, bringing the total number recognised by the city to 237,062. A few thousand names are added each year.