Hiroshima marked the 63rd anniversary of the 1945 U.S. atomic bombing Aug. 6, with the mayor announcing the city's decision to conduct a scientific study on the psychological impact the bomb left on survivors.

Doves fly by the Atomic Bomb Dome during the ceremony to mark the 63rd anniversary of the world's first atomic bombing at Hiroshima Peace Memorial Park on Aug. 6. AP PHOTO

Hiroshima Mayor Tadatoshi Akiba, presenting the Peace Decleration at a memorial service at the Peace Memorial Park, said the two-year study aims to create a complete picture of the damage caused by the bombing.

A moment of silence was observed at 8:15 a.m., the time the atomic bomb detonated over Hiroshima at an altitude of about 600 meters, killing an estimated 140,000 people by the end of 1945.

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

Attending the ceremony, Prime Minister Yasuo Fukuda pledged to firmly maintain Japan's three principles of not producing, possessing or allowing nuclear weapons on its soil.

"Today, here in Hiroshima, I again pledge that our country will firmly maintain the three antinuclear principles and to lead the international community in realizing the abolition of nuclear weapons and lasting peace," he said.

He also vowed to expand support measures for aging atomic bomb survivors.

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

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.