Japan's foreign minister on Sunday hailed UN sanctions on North Korea and said the country should provide support for the US military in inspecting Pyongyang's ships, a major step for the pacifists country.
Hours after the UN Security Council's unanimous resolution in response to North Korea's declared nuclear test, Aso said it was "only natural" for Japan to help prevent military shipments.
"The resolution calls on countries to carry them out," Taro Aso said of inspections. "It is only natural to offer our co-operation."
Japan has been officially pacifist since its World War II defeat and its help to US military operations has been confined to far-away Afghanistan and Iraq.
Under a 1999 law, Japan can provide fuel and other back-end support to US warships in "surrounding areas", but the measure has never been used.
Aso suggested Japan could take part actively in ship inspections. Asked whether Japan should limit itself to logistical support, Aso said: "I don't think so. It will depend on the situation."
But such co-operation is set to be controversial both at home and abroad.
China, which has been trying to repair sour relations with Japan, has voiced reservations about inspections on North Korean ships even though it supported the unanimous UN resolution.
China, still bitter over Japan's past aggression in the region, had criticised Tokyo's groundbreaking military mission to Iraq.
But Aso said Japan was especially threatened by North Korea, which fired a missile over Japan's main island in 1998.
"With the resolution approved, I believe the eyes of the world are on the actions of Japan, which neighbours North Korea and is likely to be the most significantly affected by the crisis," Aso said.
"Basically speaking, countries under threat from a nuclear power must defend themselves. Our job is to minimise the damage to Japan," Aso said.
The foreign minister made his comments as the policy chief of Japan's ruling party called for an active debate on developing atomic weapons.
Shoichi Nakagawa, a close aide to Prime Minister Shinzo Abe, said he did not for now support an atomic arsenal for Japan, but that "discussions should be allowed" on the subject.
But Abe reiterated that Japan -- the only nation to have suffered nuclear attack -- should not develop atomic weapons.
Abe's view comes despite his passionate support for increasing Japan's military role. Abe took office last month with rewriting the pacifist US-imposed 1947 constitution a top item on his agenda.
Japan has the world's fourth largest defence budget, but its post-World War II military is known as the "Self-Defence Forces" and has never fired a shot.
Abe, who rose to popularity by championing a tough line against North Korea, vowed Sunday that Japan "will take measures to stop the possession of any nuclear capability and nuclear proliferation."
"With the resolution, the international community has been able to send a strong message that we do not tolerate possession of nuclear weapons" by North Korea, Abe told reporters.
Abe said Japan was looking at additional sanctions it can take in line with the Security Council resolution, which demands the elimination of all North Korean nuclear weapons, weapons of mass destruction and ballistic missiles.
Japan has already imposed most sanctions at its disposal. It last week banned all North Korean imports and ships and the entry into Japan by most North Korean nationals.
Despite North Korea's pariah status, assistance to US forces so close to home is controversial in Japan and Aso said the government may ask parliament for special approval for the potential mission.
New Komeito, a Buddhist-oriented pacifist party in Abe's coalition, has reportedly been hesitant about a Japanese military role in the North Korea crisis.