South Korea warns North against second nuclear test as Rice travels to Seoul

U.S. Secretary of State Condoleezza Rice arrived in South Korea on Thursday to push Seoul to fully support sanctions against North Korea, while Chinese envoys were apparently in Pyongyang warning the reclusive country against more nuclear tests.

China could play the most important role in restraining the North because the Chinese have long been the impoverished nation's closest ally and its biggest source of trade and fuel.

Washington hoped the Chinese delegation, which included former foreign minister Tang Jiaxuan, would deliver a stern warning to the North Koreans about future nuclear tests, said a senior U.S. official speaking to reporters on Rice's plane as she traveled to Seoul from Tokyo.

"I'm pretty convinced that the Chinese will have a very strong message about future tests," the official said, adding that the United States wasn't informed ahead of time by Beijing of that mission. The official spoke on condition of anonymity, due to the sensitivity of the issue.

U.S. media have reported that satellite images showed suspicious activity at a suspected North Korean nuclear site.

The North's nuclear test last week presented a serious challenge to U.S.-South Korean ties, which have long been strained by fundamental differences about how to deal with Pyongyang. The U.S. has called for a tougher line, while South Korea has been reluctant to take moves that could inflame tensions.

The official traveling with Rice said the U.S. would try to avoid giving the South Koreans specific suggestions about how to deal with the North, reports AP.

"They don't want to be seen as being pushed," the official said.

Rice was to meet with South Korean Foreign Minister Ban Ki-moon, who warned that a second North Korean nuclear test would trigger a "much more serious" global response. Ban, slated to be the next U.N. secretary-general, also said Pyongyang shouldn't make further moves that would "aggravate the situation."