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

At the 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 World War II.

Japan submitted a resolution in the U.N. last year calling for the abolition of nuclear weapons. Akiba said that 170 nations supported it, with the U.S. as one of only three countries opposed.

"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 that included survivors, local residents and dignitaries from around the world.

Akiba addressed the crowd with the bombed-out dome of the Hiroshima Peace Memorial looming in the background, and hundreds of doves were released into the air after he finished his speech.

A moment of silence was observed at 8:15 a.m., which was the time of the blast. An estimated 140,000 people were killed instantly or died within a few months after the American B-29 bomber Enola Gay dropped its deadly payload. Japan's official death toll of nearly 260,000 includes injured who have died in the decades since.

Three days later, on Aug 9, 1945, the U.S. dropped a plutonium bomb on the city of Nagasaki, killing about 80,000 people. Japan surrendered on Aug. 15, ending World War II.

Akiba said more needs to be done for the remaining survivors, whose average age is now over 75. There are about 244,000 survivors, according to the health ministry. Many have developed illnesses caused by radiation exposure, including cancer and liver diseases.

Akiba said the two-year study is aimed at creating a complete picture of the damage caused by the bombing, which he said has not yet been revealed even after more than six decades because the effects of the atomic bomb on survivors have for years been underestimated.

"The most severely neglected have been the emotional injuries," Akiba said, in announcing the new two-year psychological study.

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

"''I, today, here in Hiroshima, again pledge that our country will firmly maintain the three antinuclear principles and take the lead in international society to realize the abolition of nuclear weapons and lasting peace,'' he said.

Some 45,000 people gathered to attend this year's ceremony in the western Japanese city, including diplomats from 55 countries.

U.N. Secretary General Ban Ki Moon said in a message read by High Representative for Disarmament Sergio de Queiroz Duarte, ''I join you in commemorating the past and affirm my determination to work with you and all people to achieve a peaceful and secure world without nuclear weapons.''

Among nuclear-power nations, China attended the ceremony for the first time, while Russia participated for the ninth consecutive year.

Meanwhile, Akiba said Mayors for Peace, a group of cities which seek to realize a nuclear-free world by 2020, proposed a Hiroshima-Nagasaki Protocol in April to supplement the Nuclear Non-Proliferation Treaty, calling for an immediate halt to all efforts to obtain or deploy nuclear weapons by nuclear-weapon states.

Among the 2,368 cities which have joined Mayors for Peace as of Aug 1, London's new mayor, Boris Johnson, has informed the group that London no longer intends to participate. The Hiroshima city is now consulting with the London mayor to persuade him to remain in the group, a city official said.

Akiba emphasized that citizens cooperating at the city level can solve man-made problems, noting that world citizens and like-minded countries have achieved treaties banning anti-personnel landmines and cluster bombs.

Japan's Constitution is ''an appropriate point of departure for a 'paradigm shift' toward modeling the world on intercity relationships from military and dominance relationships, he said.

The charter's preamble expresses the country's determination ''to preserve its security and existence, trusting in the justice and faith of the peace-loving peoples of the world.''

Akiba said, ''I hereby call on the Japanese government to fiercely defend our Constitution, press all governments to adopt the Hiroshima-Nagasaki Protocol, and play a leading role in the effort to abolish nuclear weapons.''

He also urged the government to expand support measures for aging atomic bomb survivors including those living overseas.

This year's memorial service comes amid a series of rulings against the government, with courts recognizing a number of atomic bomb survivors as suffering from atomic bomb-related illnesses, declaring illegal the government's fixed criteria that has barred many survivors from getting expanded medical benefits.

This year, the names of 5,302 more people recognized as atomic-bomb victims by Hiroshima since Aug 6 last year were added to the cenotaph at the Peace Memorial Park, bringing the total number of the city's victims to 258,310.

A total of 243,692 atomic bomb survivors were living in and outside of Japan as of March 31, with their average age at 75.14.

© Wire reports