The leader of the Nobel Peace Prize-winning antinuclear group has called for parliamentary discussions in Japan on the possibility of Tokyo signing the U.N. nuke ban treaty, warning that staying out would make the country an "outlier" of the global disarmament movement.

Beatrice Fihn, executive director of the International Campaign to Abolish Nuclear Weapons, told representatives of nine political parties and the government in an open forum Tuesday that Japan needs to abandon its defense policy relying on the umbrella of U.S. nuclear deterrent, calling it an "outdated" theory based on the threat of actual use of nuclear weapons.

The Japanese government has said it is sitting out of the treaty, citing the need for U.S. nuclear deterrence to "protect the lives and properties of Japanese citizens in the face of growing and realistic nuclear threat from North Korea."

"Nuclear deterrence did nothing to stop North Korea's nuclear ambitions. Instead, it has fueled it," Fihn said in Tokyo.

"It is clear that nuclear deterrence is a myth. It does not work, it did not deter North Korea from developing their own nuclear weapons. It encouraged proliferation. We can solve this crisis with the nuclear ban treaty."

"Japan can join this treaty while keeping the military alliance with nuclear armed states like the United States," she said, noting that the treaty urges a signatory to commit "to not using, not producing, not possessing nuclear weapons and not encouraging or assisting the use of nuclear weapons."

"Every responsible state that respects human rights and humanitarian law should do that," she said.

On the proposed launch of discussions in the parliament, Fihn cited examples in Italy and Norway, members of the North Atlantic Treaty Organization, as well as Sweden and Switzerland, which have started considering the treaty as an option for disarmament.

"I urge (the Japanese parliament) to start an investigation that would look at the prohibition (treaty) and how that relates to the activities that Japan is doing," she said. "The stakes are too high to not explore this option for nuclear disarmament and right now with the increasing threats of nuclear war (posed by North Korea) the treaty is the best path forward."

In the forum, Masahisa Sato, senior vice foreign minister, reiterated the government's stance against signing the treaty, citing the lack of its support by major countries possessing nuclear weapons and saying that joining the pact "would deny the legitimacy of the Japan-U.S. alliance and the nuclear deterrence."

Keizo Takemi, representing the ruling Liberal Democratic Party headed by Prime Minister Shinzo Abe, was also cautious about the treaty, saying, "We must make diplomatic efforts morally, but at the same time respond to real military threats" posed by North Korea.

ICAN, founded in 2007, is a coalition of nongovernmental organizations that involves about 470 groups from more than 100 countries. It received the Nobel Peace Prize for their efforts that led to the adoption of the U.N. nuclear ban treaty in July last year.

Fihn traveled to Tokyo after visiting Hiroshima and Nagasaki, which were devastated by U.S. atomic bombings in 1945, on her first visit to Japan.