Tadatoshi Akiba said Washington's apparent worship of "nuclear weapons as God" was threatening world peace.
"The Nuclear Non-Proliferation Treaty, the central international agreement guiding the elimination of nuclear weapons, is on the verge of collapse," Akiba said during the annual ceremony at the Peace Memorial Park. "As the U.S.-British-led war on Iraq made clear, the assertion that war is peace is being trumpeted as truth."
At 8:15 a.m., a bell tolled, marking the minute on Aug. 6, 1945 when the U.S. atomic bomb's explosion devastated this city, 429 miles southwest of Tokyo. For 60 seconds, tens of thousands of survivors, residents, activists and officials from around the world bowed in silence to commemorate the 160,000 people who were killed or injured in the blast.
Reminding the crowd of the "blazing hell fire that swept over this very spot 58 years ago," Akiba called all nuclear weapons "utterly evil, inhumane and illegal under international law."
This year's ceremony comes less than a week after North Korea agreed to U.S. demands for six-nation talks to resolve the standoff over the isolated communist regime's nuclear programs. China, Russia, Japan and South Korea were expected to take part, though no timeline for the meetings has been decided.
Akiba didn't directly criticize Pyongyang's nuclear ambitions. But he urged North Korean leader Kim Jong Il, President Bush and the heads of other nuclear-armed countries to visit Hiroshima and confront the nuclear attack's aftermath.
The Bush administration wants Congress to approve $68 million for research into advanced nuclear weapons technology, including research on a ground-penetrating nuclear warhead, known as a bunker-buster, and smaller, so-called mini-nukes, of less than 5 kilotons.
It also wants to conduct research on how nuclear testing might be restarted, if necessary. The United States has had a self-imposed ban on nuclear testing since 1992, and the White House says it has no current plans to resume testing.
During Wednesday's ceremony, Prime Minister Junichiro Koizumi reaffirmed Japan's policy banning the production, possession and transport of nuclear weapons within its borders.
"Our country's stance on this will not change," Koizumi said, adding that Tokyo would push for countries to ratify the Comprehensive Test Ban Treaty, which would impose a moratorium on nuclear explosion tests.
Afterward, thousands of people lined up in the sweltering heat to burn incense, pray and shoot photographs at the arch-shaped stone memorial, which contains the names of hundreds of thousands of people who were in the city on the day of the bombing.
Hiroshima city added to the cenotaph 5,050 names of those who have died from cancer and other long-term ailments over the past year, raising the toll to 231,920, city official Yukiko Ota said.
Ceremonies will be held Saturday on the anniversary of the atomic bombing of Nagasaki, on the southernmost main island of Kyushu. About 70,000 people were killed by an atomic bomb dropped on Nagasaki from a U.S. aircraft, three days after the one that leveled Hiroshima.
Six days later, on Aug. 15, 1945, Japan's surrender ended World War II.
While no nuclear weapon has been used in combat since 1945, in the intervening 58 years seven other countries have obtained "the bomb" — Britain, China, France, India, Israel, Pakistan and Russia.
According to the Arms Control Association, four countries — Iran, Iraq, Libya and North Korea — are "of immediate concern" as states that may soon acquire nuclear weapons.