Japan has decided to impose fresh sanctions on North Korea in response to its reported nuclear test earlier this week, and its apparent plans for a second, public broadcaster NHKreported.
The decision is expected to be formalised at a meeting of Japan's National Security Council later today.
Cabinet ministers gathered at the prime minister's office today but declined to comment on whether they had decided on new sanctions in addition to those imposed after North Korea fired a salvo of missiles in early July.
Japan has joined with the United States in calling for tough sanctions by the UN Security Council to pressure Pyongyang to abandon its nuclear programme.
North Korea announced on Monday that it had conducted its first-ever nuclear test. It says a US "threat of nuclear war and sanctions" forced its hand.
Japanese Foreign Minister Taro Aso told a parliamentary panel that Japan had unconfirmed information that the communist state might conduct another test today.
South Korea's Vice Foreign Minister Lee Kyu-hyung said in Seoul that his government, which has shied away from sanctions in the past, supported the discussions in the UN Security Council.
"We hope that related countries can express in one voice a clear and firm position on North Korea's peace-destroying and provocative act through close consultations," he told reporters
South Korea's Joint Chiefs of Staff urged a review of the nation's readiness for nuclear war, Yonhap said.
China and Russia, which both border North Korea, met other veto-holding members of the UN Security Council yesterday to discuss a range of sanctions proposed by the US and Japan.
"I think that there has to be some punitive actions," said Beijing's UN ambassador, Wang Guangya. "We need to have a firm, constructive, appropriate but prudent response to North Korea's nuclear threat."
Russia called Monday's reported test a "colossal blow" to the non-proliferation regime but, like China, insisted an eventual UN resolution should not involve the use of force.
UN diplomats said China has proposed citing specific provisions in the UN Charter to make sure any sanctions excluded any hint of military action.
China has very strong trade ties with North Korea and has traditionally been the reclusive Stalinist state's closest ally in the region.
Japanese government officials have said sanctions could include barring all North Korean ships from entering Japanese ports and banning all trade between Japan and North Korea.
Economists said the effect on North Korea of banning trade would be more symbolic than real unless Pyongyang's key trading partners such as China and Russia joined in.
"The impact from sanctions by the Japanese alone would be very small. But Japan cannot do nothing, because it faces the biggest threat, and sanctions would have a political meaning," said Mitsuhiko Kimura, an economics professor at Aoyama Gakuin University in Tokyo.
In September, Japan approved new financial sanctions to effectively freeze remittances and the transfer of funds from Japan by groups suspected of having links to North Korea's missile and weapons of mass destruction programmes.