Updated

The mayor of Hiroshima called Sunday for the elimination of all nuclear weapons as he marked the 61st anniversary of the world's first atomic bomb attack, which killed more than 140,000 people in the Japanese city.

Expressing concerns over the global proliferation of nuclear weapons, Mayor Tadatoshi Akiba urged the government of Japan — the only nation to suffer atomic bomb attacks — to take a leading role in the effort to eliminate nuclear arsenals.

"Sixty-one years have passed since radiation, heat rays and an atomic blast created hell on earth," Akiba said in a speech at Hiroshima Peace Park, near the bomb's epicenter. "But the number of nations enamored of evil and enslaved by nuclear arms has increased. The only role nuclear weapons have is to be demolished."

A bell rang at 8:15 a.m., marking the time when the American B-29 bomber Enola Gay dropped its deadly payload on Hiroshima on Aug. 6, 1945. It was the first atomic bomb ever used in war.

About 45,000 survivors, residents, visitors and officials from around the world prayed for the bombing victims by observing a minute of silence in Hiroshima, 690 kilometers (430 miles) southwest of Tokyo. Hundreds of doves were released afterward.

An estimated 140,000 people were killed instantly or died within a few months after the bombing. Three days later, another U.S. warplane dropped a plutonium bomb on the city of Nagasaki, killing about 80,000 people.

This year's anniversary comes amid concerns over North Korea's recent missile tests, stalled six-nation talks on its nuclear weapons program, and intensified fighting in the Middle East.

Akiba urged Japan, a participant in the six-nation talks, to "forcefully insist that nuclear arms-possessing nations fulfill their obligation to sincerely carry out negotiations aimed at nuclear disarmament."

He also urged the government to observe Japan's pacifist Constitution, which bars the use of force in international disputes and prohibits Japan from keeping a military for warfare. It was drafted by U.S. occupation forces after World War II and has not been changed since 1947.

Prime Minister Junichiro Koizumi's ruling party is proposing constitutional changes to make it easier for the Japanese military to fight if it comes under attack and to participate in international peacekeeping.

Koizumi said in a memorial speech Sunday that "We will observe the pacifist clause of the Constitution, maintain the principle of nuclear non-proliferation and lead international efforts to achieve lasting global peace."

Ceremonies will also be held on Wednesday's anniversary of the Nagasaki attack.

Japan surrendered on Aug. 15, 1945, bringing World War II to an end.