Japanese Prime Minister Shinzo Abe called on Wednesday for painful sanctions on North Korea even if its declared nuclear test turned out to be a failure.
Abe, who rose to prominence as a hardliner on North Korea, said that planned bilateral sanctions would have a sizable impact on the impoverished state.
"We have to take considerable measures against their announcement," Abe said. "I presume they also expect them to be considerable as the sanctions will be imposed by my government."
Japan has already slapped most of the sanctions at its disposal against North Korea, which conducts the bulk of its limited trade with China and South Korea.
Japan banned a major North Korean ferry link, visits by diplomats and charter flights in response to Pyongyang's missile tests in early July.
The Abe government is now considering banning all imports from North Korea, refusing new entry of North Korean nationals and prohibiting all North Korean ships from making port calls to Japan, local media said.
Abe, who took office last month, said it made no difference whether the international community confirms North Korea's announcement on Monday that it had tested its first atom bomb.
"Even if it's a failure, that means they attempted to conduct a nuclear test," Abe told parliament.
"There is no difference in the weight of guilt," he said. "We have to consider our own measures by making a comprehensive decision."
Japan has also backed US calls for the UN Security Council to slap far-reaching sanctions on North Korea.