Japanese leaders called for a shift away from nuclear power at a solemn ceremony Tuesday marking the 66th anniversary of the atomic bombing of Nagasaki.

About 6,000 people, including diplomats from 44 countries, gathered in the city's Peace Park to hear a bell toll at the exact moment the bomb fell 66 years ago. The ceremony included prayers and a reading of the names of bomb survivors who died in the past year.

Nagasaki Mayor Tomihisa Taue appealed in his formal remarks for Japan to find sources of renewable energy to replace nuclear energy. He said it is time for the Japanese people to debate what kind of society they want to live in.

Prime Minister Naoto Kan, in his own remarks, expressed deep remorse for the failure of existing nuclear policies to protect the public from the accident at the Fukushima nuclear plant. He agreed that Japan must move away from its reliance on nuclear power.

James Zumwalt, the charge d'affaires at the U.S. embassy in Tokyo, became the first U.S. official ever to attend the annual event. He said his presence reflected the desire of President Barack Obama to rid the world of nuclear weapons.

U.S. Ambassador John Roos attended a similar ceremony last year in Hiroshima, one of two cities attacked with U.S. atomic bombs in the closing days of World War II. Roos was not able to attend the Nagasaki event because of scheduling difficulties.

Nagasaki officials say the bomb killed 74,000 people and injured 75,000 by of the end of 1945. Thousands more died of radiation-related illnesses in the following years.