HIROSHIMA - Hiroshima's mayor on Wednesday urged the next U.S. president to support a proposed ban on nuclear weapons, as Japan marked the 63rd anniversary of the atomic blast that obliterated this city and killed 140,000 people.

In a ceremony, Hiroshima Mayor Tadatoshi Akiba also announced the launch of a two-year study to gauge the psychological toll of the Aug. 6, 1945, attack in the closing days of the Second World War.

Japan submitted a resolution in the U.N. last year calling for the abolition of nuclear weapons. Akiba said that 170 nations supported the resolution, while the united States was one of only three countries to oppose it.

"We can only hope that the U.S. president elected this November will listen conscientiously to the majority," Akiba told a crowd of 45,000 gathered beneath at the spot where the bomb detonated.

A moment of silence was observed at 8:15 a.m., the time of the blast. An estimated 140,000 people were killed instantly or died within a few months after the bombing. Japan's official death toll of nearly 260,000 includes injured who have died in the decades since.

Three days later, another U.S. airplane dropped a plutonium bomb on the city of Nagasaki, killing about 80,000 people. Japan surrendered less than a week later, on Aug. 15, ending the Second World War.

Prime Minister Yasuo Fukuda also spoke at the ceremony, emphasizing Japan's continued policy against using nuclear weapons or allowing them onto its territory.

Ceremonies will be held on Saturday in Nagasaki.