Countries from China to Germany have urged North Korea to return to talks on ending its nuclear programs after Pyongyang announced it has nuclear weapons and pulled out of disarmament talks.

The move presents a serious challenge to the United States and President GeorgeWBush, starting his second term with a policy aimed at ending north Asia's nuclear crisis through the six-party talks that China has been shepherding for nearly two years.

China, South Korea and Germany Friday joined calls from Washington and around the world for Pyongyang to resume negotiations. Standing in the firing line is South Korea, under constant threat from a neighbor that keeps 70 percent of its 1.2-million-strong army on a border that passes 65 kilometers north of the capital, Seoul.

``The assessment is that North Korea may be trying to raise its negotiating stakes,'' South Korean Vice-Foreign Minister Lee Tae Shik said.

``But it could turn into a very serious problem if the North takes additional steps.''

North Korea's Foreign Ministry declared Thursday the country was forced to boost its defenses and to acquire nuclear weapons to contend with US hostility and the policy of the Bush administration to seek regime change.

It pulled out of the six-way talks, which also involve the United States, China, Russia, Japan and South Korea, but left the door open slightly to a possible resumption of negotiations.

South Korean officials joined the United States in saying talks are the only solution to end the North's isolation, though Foreign Minister Ban Ki Moon, visiting Washington, said Seoul could not tolerate a nuclear-armed North.

As for Japan, Prime Minister Junichiro Koizumi said his nation - seen by experts to be in range of North Korean missiles - will use the power of persuasion ``by presenting it with a case that its interests are best served by dismantling its nuclear programs.''

China, one of North Korea's few friends and the country that exercises the most influence there, issued a brief response that it hoped talks would continue and is watching developments.

Australia, one of the few Western countries to have official ties with the North, moved to mediate. Foreign Minister Alexander Downer said he had spoken with North Korean ambassador to Canberra Chon Jae Hong and US Secretary of State Condoleezza Rice.

``I took some encouragement from the fact that although [Chon] thought the climate wasn't right at the moment, that implied that matters could change,'' he said.

Some analysts said North Korea might be raising the stakes while US attention is focused on Iran's nuclear programs in order to obtain better terms. North Korea has engaged in brinkmanship in the past at crucial junctures.

Three rounds of six-party talks have been held since August 2003, but a fourth failed to start in September as the North Koreans refused to show up. Bush has backed a diplomatic solution to the crisis but now faces two nations he once named as part of an ``axis of evil'' being defiant about their nuclear programs - North Korea and Iran. Iraq was the third ``axis'' nation.

Pyongyang sent a message of solidarity to Iran Thursday on the 26th anniversary of the Islamic Republic to praise its success in working to defend its sovereignty.

``North Korea's rejection of dialogue is the worst possible choice,'' South Korea's conservative Dong-A Ilbo said in one of several strong commentaries that appeared in Seoul Friday. ``The North's Foreign Ministry statement has changed the nature of the nuclear issue. North Korea may be thinking that it can control the nuclear issue. That would be a gross mistake.''

Ralph Cossa, president of the Pacific Forum CSIS think-tank, said the North had crossed an important threshold and Washington must ensure it is on the same page as its allies because divisiveness will play into the North's hands.

It would seem ``foolish, and foolhardy, to ignore the intended message,'' he said. ``This sounds to me like an unambiguous declaration by North Korea that it is a nuclear-weapons state.''

Rice said Washington had assumed since the mid-1990s that North Korea could make nuclear weapons, though Defense Secretary Donald Rumsfeld said he did not know whether it did indeed have a bomb.

Experts said North Korea likely had produced enough plutonium for up to eight weapons, but no one could be sure if it could assemble and deliver one.

South Korean Foreign Ministry spokesman Lee Kyu Hyung said Seoul's assessment of the North's nuclear capability remained unchanged at ``material for up to three bombs.''