Washington ? North Korea’s declared determination to become the world’s eighth nuclear power has prompted a flurry of U.S. diplomatic activity as the Bush administration, its policy of engagement with Pyongyang discredited, ponders its next steps.

Undersecretary of State John Bolton met Thursday with officials in China, a major trading partner of North Korea’s and perhaps the one country capable of extracting concessions from the communist nation through economic sanctions, an administration official said.

At the White House, reporters were told the Chinese were stunned upon learning of North Korea’s acknowledgment to U.S. officials that it was pursuing a nuclear weapons program.

A U.S. delegation had confronted North Korea with evidence gathered over the last several months, including recent bills of sale, that Pyongyang had been working to enrich uranium for nuclear weapons. That equipment most likely was part of a gas centrifuge program to separate the weapons-grade uranium from ordinary fuel-grade uranium, private analysts said Thursday.

North Korea’s earlier nuclear efforts relied on plutonium, which makes smaller, lighter bombs but is much more difficult to produce and work with than enriched uranium.

White House spokesman Scott McClellan said President Bush thought North Korea’s admission was “troubling, sobering news.” He said Bush was seeking a peaceful solution.

Privately, White House officials said Bush and his senior advisers decided to confront the problem in a low-key fashion. Bush, for example, made no public statements on it Thursday.

Stressing the diplomatic approach, National Security Adviser Condoleezza Rice said, “I think were going to see that no one wants to have a nuclear-armed North Korea and that effective international pressure may have an effect on North Korea.”

China, Russia, Japan and South Korea are among the countries that have a stake in a nuclear-free North Korea, Rice said in an interview for the Thursday edition of ABC’s “Nightline.”

It was not clear to U.S. officials whether North Korea actually has a nuclear capability or whether it is still in development. At a minimum, North Korea apparently is close to joining the United States, China, Russia, Britain, France, India and Pakistan as declared nuclear powers.

Israel is thought to have hundreds of nuclear warheads but has never confirmed it has a nuclear weapons program.