His criticism came on the 59th anniversary of the world's first atomic bombing which killed tens of thousands of people in this Japanese city.
"The egocentric world view of the US government is reaching extremes," Mayor Tadatoshi Akiba said on Friday at the ceremony held against the backdrop of the Atomic Bomb Dome, the preserved ruins of one of the few buildings not flattened by the blast.
Iraqi Doctor Hussam Salih was among those present. From Basra, Salih is in Hiroshima studying cancer and leukemia treatments.
"Ignoring the United Nations and its foundation of international law, the United States has resumed research to make nuclear weapons smaller and more usable," the mayor told 45,000 people at the Hiroshima Peace Memorial Park.
Chain of violence
Meanwhile, a chain of violence and retaliation around the world showed no sign of ending, he said.
"Reliance on violence-amplifying terror and North Korea, among others, buying into the worthless policy of 'nuclear insurance' are salient symbols of our times," he said.
Around 140,000 people died from
both direct and indirect fallout
Prime Minister Junichiro Koizumi meanwhile pledged that Japan would stick to its post-1945 war-renouncing constitution.
As the clock clicked onto 8:15 am (2315 GMT Thursday), the exact time the US dropped the bomb codenamed Little Boy, those at the ceremony bowed their heads for a minute's silence in memory of victims of the attack.
Around 140,000 people - almost half the city's population of the time - died immediately or in the months after the dropping of the 20 kiloton atomic bomb, from radiation injuries or horrific burns.
During Friday's ceremony officials added to the existing toll the names of 5142 atomic bomb sufferers who died or were confirmed dead during the past year.
The additions brought the cumulative death toll associated with the effects of the bombing to 237,062.
The Hiroshima bombing was followed by the dropping of a second atomic bomb on the city of Nagasaki on 9 August 1945, leaving tens of thousands more dead.
"We have to pass
stories of our suffering from generation to generation and appeal more to the public about the terrible nature of nuclear weapons"
Sunao Tsuboi, head of Hiroshima Prefectural Confederation of A-Bomb Sufferers Organisations
The appalling loss of life among ordinary Japanese was credited with forcing Japan to surrender six days later, ending the second world war II in the Pacific theatre.
The mayor also declared the period from Friday to 9 August 2005 to be a year of "Remembrance and Action for a Nuclear-Free World", while calling on Americans to act as "a people of conscience".
The head of a group of survivors of the bombs said they were "boiling with anger" over global stockpiles of nuclear weapons and the spreading violence since the September 2001 attacks.
"We have a grave duty in today's critical situation ...," Hiroshima Prefectural Confederation of A-Bomb Sufferers Organisations head Sunao Tsuboi said.
"We have to pass stories of our suffering from generation to generation and appeal more to the public about the terrible nature of nuclear weapons," he said.