A key member of an international organization that won this year's Nobel Peace Prize criticized Wednesday the Japanese government for effectively ignoring a landmark U.N. treaty that outlaws nuclear weapons.

"This extraordinary silence on this treaty by the Japanese government is very, very disappointing and frustrating," Akira Kawasaki of the International Campaign to Abolish Nuclear Weapons said at the Foreign Correspondents' Club of Japan.

ICAN won the prize last week for its efforts that led to the adoption in July of the Treaty on the Prohibition of Nuclear Weapons.

But the statement released by the Japanese Foreign Ministry about the award did not mention the treaty, Kawasaki said, adding that Tokyo is also expected to submit a draft U.N. resolution on nuclear disarmament without referring to the treaty.

Along with the world's nuclear weapons states, Japan did not sign the treaty, which was adopted by 122 U.N. members, as it relies on the U.S. nuclear deterrence for protection.

Kawasaki, an ICAN International Steering Group member and a co-chair of Japanese nongovernmental organization Peace Boat, also said that supporting the treaty will help Japan in dealing with threats from North Korea's nuclear and missile development.

The treaty "delegitimizes North Korean actions on nuclear weapons," he said.

Sueichi Kido, 77, who suffered the 1945 U.S. atomic bombing in Nagasaki at the age of 5, also attended the press conference as ICAN has been working with hibakusha atomic bomb survivors in its campaign.

The fact that Japan did not sign the treaty "is not only embarrassing and sad but also makes me very angry," Kido said.