The only country to have been attacked with an atomic bomb is facing growing calls to observe the first meeting of signatories to a treaty banning nuclear weapons.

Japan, however, relies on the U.S. nuclear umbrella for its security and is not one of the treaty's 86 signatory countries and regions

"We urge the government of Japan ... to swiftly sign and ratify the treaty," the Japan Confederation of A- and H-Bomb Sufferers Organizations said in a statement released Saturday, the first anniversary of the treaty's entry into force.