South Korea's foreign minister has cautioned against pushing North Korea into a corner on its nuclear weapons programs, but he also warned the North against testing a nuclear explosive.

Ban Ki-moon

Foreign Minister Ban Ki-moon Friday reiterated his warning against a North Korean nuclear test, saying it could only worsen tensions on the Korean peninsula.

Ban says, if North Korea forges ahead with a nuclear test, it will have "far more serious repercussions than the recent missile launches."

Pyongyang defied warnings from its neighbors last month, and test-fired seven missiles. That led to United Nations sanctions and a halt to important South Korean economic aid to the impoverished North.

Ban, who was speaking to foreign journalists in Seoul, said the international community should be firm in denouncing North Korea's bad behavior. But, he said, at the same time, other countries should refrain from cornering Pyongyang into "a dead end with no way out."

He added that the chances of resuming three-year-old negotiations on ending the North's nuclear programs have deteriorated since last month's missile launches.

In Tokyo, Japanese Chief Cabinet Secretary Shinzo Abe said a nuclear test would be "absolutely unacceptable," and would pose a "grave threat" to Japan's peace and stability.

North Korea says it has nuclear weapons and both the South Korean and U.S. governments think it has at least one or two nuclear bombs. So far, however, it has never exploded a nuclear device. U.S. and Japanese news reports say Pyongyang may be preparing to do an underground nuclear test.

South Korea, Japan, the United States, China and Russia have been trying to persuade North Korea to abandon its nuclear programs in exchange for economic and security guarantees. Pyongyang agreed in principle to do that last September, but has since boycotted negotiations, demanding that U.S. sanctions over its alleged illegal financial activities be lifted. The United States wants Pyongyang to return to the talks without conditions.

Even without the nuclear tests, sanctions are already pushing the North into further isolation. On Friday, Japan refused to allow six North Koreans to enter the country for a religious conference.

Japanese Justice Minister Seiken Sugiura says the decision is based on Japan's strict immigration screening on North Korean nationals since the missile launches.

North Korean leader Kim Jong Il is reportedly traveling to China - his country's main ally - next week to meet with Chinese officials. But the missile launches and concerns over a nuclear test are straining ties with Beijing. Regional political experts say Pyongyang's behavior could make it harder for China to continue supporting it militarily.