Japan, the only country to suffer a nuclear attack, won't sign the United Nations' Treaty on the Prohibition of Nuclear Weapons.

Signed by 84 countries and ratified or acceded to by another 50, the treaty is now a binding international accord. It comprehensively bans nuclear weapons. There are 193 UN member states.

The government of Prime Minister Yoshihide Suga said Japan won't sign the treaty and doesn't welcome its coming into force in 2021. Its decision rejects appeals from atomic-bomb survivors in Japan who encouraged Suga to work for a nuclear-free world.

Chief Cabinet Secretary Katsunobu Kato said "Japan's approach is different from that of the treaty and there is no change to our position not to sign it," according to the latest news reports. "We doubt if support is growing even among nonnuclear weapons states, let alone nuclear weapons states."

Japan has said it wasn't realistic to approve the treaty when nuclear powers and nonnuclear states remained divided over nuclear weapons. Kato said Japan had chosen to serve as a bridge between the two sides.

Political experts said a reason for Japan opposing the treaty was that it remained protected by the U.S. "nuclear umbrella" against threats from North Korea and China.

"We need to appropriately respond to the current security threats, by maintaining or strengthening our deterrence," noted Kato. "We have to be realistic about promoting nuclear disarmament."