Japan – Japan's main opposition Democratic Party, which has a good shot at winning power in a general election this month, said on Thursday it backed U.S. President Barack Obama's call to rid the world of nuclear arms.

In the western city of Hiroshima to remember the victims of the world's first atomic attack in 1945, party leader Yukio Hatoyama also said Japan should appeal to world leaders to eschew nuclear arms.

Prime Minister Taro Aso, his Liberal Democratic Party's poll ratings sagging ahead of the August 30 poll, reaffirmed Tokyo's self-imposed ban on nuclear weapons.

Tensions in the region were heightened in May when neighboring North Korea conducted a nuclear test.

Realizing a nuclear-free world as called for by U.S. President Obama is exactly the moral mission of our country as the only atomic-bombed state, Hatoyama, quoted by Kyodo news agency, told a ceremony marking the 1945 attack.

He was backed by the mayor of Hiroshima, where more than 260,000 people died from the bomb, either from the blast or later from the effects of the nuclear explosion.

Japan often refers to its position as the only country to suffer nuclear attacks when calling for the abolition of atomic weapons. The United States dropped a second atomic bomb on the southern city of Nagasaki days after the attack on Hiroshima.

While many in Japan oppose nuclear arms, Tokyo benefits from the shelter of a nuclear umbrella extended by its biggest ally, Washington.

Aso said Japan stood by its fundamental non-nuclear principles and take the lead within the international community to abolish nuclear weapons and bring about lasting peace.

But, speaking to reporters after attending the main commemorations, he said the nuclear umbrella was vital as it was unlikely all nuclear powers would give up nuclear arms at once.

It's hard to say that a country will abandon (nuclear weapons) right away when another does, he said.

A former government official said in recent interviews that Tokyo had secretly agreed with Washington in 1960 that Japan would allow stopovers by U.S. military aircraft or vessels carrying nuclear weapons. Japan denies having made such a deal.

More than 1,000 people gathered for a protest in central Hiroshima against the use of nuclear weapons. Many had come to protest against an anticipated speech by a former air force official who has called for Japan to be a nuclear power.

Toshio Tamogami was fired as air force chief of staff last year after he wrote an essay arguing Japan had not been an aggressor in World War Two. He was set to appear at an event hosted by a lobby group that backs traditional values.

(Writing by Chisa Fujioka, Isabel Reynolds, editing by Ron Popeski)