South Korea and China have agreed to cooperate to prevent a possible nuclear test by North Korea amid increasing reports citing suspicious activity in the communist nation, Seoul's presidential security adviser said Friday.
A nuclear test by the communist North would be "a grave situation of a different level from missile launches," Song Min-soon said after returning from a two-day trip to China, South Korea's Yonhap news agency reported.
"South Korea and China have agreed to continue cooperation not to let that situation occur," Song was quoted as saying.
The North stoked regional tensions last month by test-firing seven missiles, drawing U.N. Security Council sanctions, and concerns are growing that it could be preparing for a nuclear test.
Japan's Kyodo News agency reported late Thursday that vehicles were seen in recent days at what is thought to be a nuclear testing site in northeastern North Korea. That followed a U.S. television report last week of other suspicious activity at a possible test site.
The Japanese government's top spokesman, Chief Cabinet Secretary Shinzo Abe, declined Friday to confirm the report, saying he could not comment on what Japan knows because of intelligence reasons, but urged North Korea to return to stalled six-nation talks on its nuclear disarmament.
"If North Korea does carry out its nuclear experiment, it will pose a grave threat to the peace and security of Japan, Northeast Asia, and the international community," Abe said in Tokyo. "It will be absolutely unacceptable."
Japan's Foreign Ministry said that Tokyo had boosted surveillance of the area, but defense officials also refused to comment on the Kyodo report.
South Korean Foreign Minister Ban Ki-moon said Friday that Seoul was "closely monitoring North Korea's movements" in cooperation with the U.S. and other countries.
Ban warned other countries against backing North Korea into a corner while seeking to stop its nuclear weapons aspirations.
"We need to exhibit resolve in denouncing North Korea's bad behavior whilst having the wisdom not to corner North Korea into a dead end with no way out," Ban told foreign correspondents in Seoul.
Meanwhile, South Korea's defense minister said Friday that North Korea is believed to have one or two nuclear weapons.
The comments by Yoon Kwang-ung to a parliamentary meeting were seen as a change in South Korea's assessment of the North's nuclear forces, with Seoul previously saying only that the North had the "capability" to build one or two nuclear weapons.
South Korea has been cautious of its assessments on the neighboring North, seeking to minimize tension as it maintains its engagement with Pyongyang. Most experts believe the North has enough radioactive material for at least a half-dozen bombs.
The North has said it won't return to international nuclear talks until a Macau bank where it held accounts is removed from a U.S. blacklist, which would free the regime's money now frozen by the bank.
The U.S. argues the issue is separate from the nuclear talks, but that it could discuss that and other concerns if the North returns to the six-nation negotiations, which also include China, Japan, Russia and South Korea.
South Korea's Song said he discussed with Chinese Foreign Minister Li Zhaoxing "how they could cooperate" to find solutions to the standoff over the North's nuclear program, according to Yonhap.
Ban said the South Korean government "is in close consultation with all the other parties at the six-party talks, including the United States, to find a flexible and creative way out of the current stalemate situation." He didn't elaborate.