HIROSHIMA (Kyodo) Prime Minister Taro Aso stressed on Thursday the need for Japan to stay under the U.S. nuclear umbrella, while opposition leader Yukio Hatoyama supported President Barack Obama in seeking a nuclear-free world.

"Located next to a country possessing nuclear arms and thinking of making an attack by using them, Japan is in alliance with the United States, which tries to use its nuclear arsenal as a deterrence," Aso told reporters, referring to North Korea, after attending Hiroshima's annual ceremony marking the atomic bombing.

"It is not true to say if someone unilaterally abandons them, everyone else will follow," Aso said. "It is unimaginable that nuclear weapons will be altogether abolished around the world."

Aso made the comments while reiterating that Japan seeks a nuclear-free world.

"Realizing a nuclear-free world as called for by U.S. President Obama is exactly the moral mission of our country as the only state to have been hit with atomic bombs," said Hatoyama, president of the Democratic Party of Japan.

At a ceremony in Hiroshima organized by the Japan Confederation of A- and H-Bomb Sufferers Organizations, Hatoyama said Japan should lead the world in efforts to abolish nuclear arms, particularly at the coming U.N. review conference of the Nuclear Nonproliferation Treaty next May.

He said to attain that goal, it is important to appeal directly to leaders of other countries, and he is willing to work for an early realization of the Comprehensive Test Ban Treaty and the Fissile Material Cutoff Treaty.