Foreign Minister Taro Aso said on Wednesday that Japan is ready to summon the UN Security Council again and press for harsher sanctions on North Korea if it carries out another nuclear test.
"Japan, as the chair country, would summon the UN Security Council," Aso told a parliamentary foreign affairs committee when asked about a potential new test.
"It would lead to more severe sanctions based on the earlier resolution," he said.
North Korea conducted its first-ever nuclear test on October 9, leading to world-wide outrage, including a UN Security Council resolution imposing sanctions on the communist state.
Japan has also imposed its own sweeping sanctions, banning all imports and ships from North Korea, and considers expanding bans on cash flow to the country.
Tokyo also plans to prohibit exports of luxury goods, suspecting they would be used by the North Korean dictatorship.
Aso had said Tuesday that he had received unspecified information that North Korea was preparing for another nuclear test, but told the parliamentary committee Wednesday he had no further details.
"I was informed that they would go ahead to conduct another one soon, but there is a variety of mixed information," he said. "Honestly, since it's underground, it's not visible from outside."
NBC News, citing unnamed US officials, said that the North Korean military had informed China that it plans to conduct a series of underground nuclear tests.
Japan's top government spokesman Yasuhisa Shiozaki said Tokyo had not heard anything from Beijing.
"Even though we have been exchanging information with China very closely, the government at this point does not have that kind of information," Shiozaki told a news conference.