Japan has joined the United States and the Republic of Korea (ROK) in agreeing not to recognize the Democratic People's Republic of Korea (DPRK) as a nuclear weapons state, the Japanese Foreign Ministry said Monday.

Tokyo's position was agreed to during a brief evening phone conversation between Foreign Minister Taro Aso and US Secretary of State Condoleezza Rice, the Foreign Ministry said in a statement.

The two diplomats said they would also consult with China, Russia and the ROK on the DPRK nuclear standoff on the sidelines of the Asia-Pacific Economic Cooperation summit later this month in Viet Nam.

The announcement comes hours after the United States and South Korea said they would refuse to treat the DPRK as a nuclear state, indicating a difficulty that lies ahead when disarmament talks resume with Pyongyang.

Seoul and Washington also agreed during high-level talks on the need for "full and effective" implementation of a UN sanctions resolution against Pyongyang for conducing a nuclear test. But they made no mention of a US initiative primarily aimed at the North that seeks to stem the proliferation of weapons of mass destruction by stopping ships suspected of trafficking.

The US has said it wants the South to increase its participation in the US-led Proliferation Security Initiative and UN sanctions banning the country's weapons trade, but so far Seoul has only sent observers to exercises under the programme.

The talks yesterday included Nicholas Burns, US undersecretary of state for political affairs, and Robert Joseph, US undersecretary of state for arms control and international security.

"Both parties shared the view that North Korea's (DPRK's) nuclear test is a grave threat to peace and security on the Korean Peninsula, Northeast Asia and beyond," the US and the ROK said in a statement after the talks. "Both parties reaffirmed the position that North Korea will not be recognized as a nuclear weapon state."

Meanwhile, there were signs of disagreements between Seoul and Washington on how hard to press the North. Seoul has been struggling to strike a delicate balance between its obligations to punish the North under the UN sanctions resolution, and concerns that aggravating its volatile neighbour could destabilize the region.

"Let me confess that many challenges are ahead of us. We need confidence in our alliance," ROK Vice-Foreign Minister Yu Myung-hwan said at the start of a meeting with Burns.