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U.S. President Barack Obama speaks about the North Korean nuclear test in the Rose Garden of the White House in Washington, D.C. - 


Bob Moon: North Korea's defiant test of that nuclear bomb has prompted international condemnation and calls for stiffer sanctions. But even amid great economic and political turmoil, isolation doesn't seem to be working, and money doesn't seem to be talking. So what options does that leave the U.S. and its allies? Here's our Washington bureau chief John Dimsdale.

JOHN DIMSDALE: The Obama administration came into office offering to engage North Korea with high-level talks. That ended when the North tested a long-range missile last month. And today, President Obama took time out from his Memorial Day rounds to accuse North Korea of ignoring its own commitments to abandon nuclear weapons.

PRESIDENT BARACK OBAMA: Its actions have also flown in the face of United Nations resolutions. As a result North Korea is not only deepening its own isolation, it's also inviting stronger international pressure.

Those U.N. sanctions did nothing to deter North Korea's nuclear ambitions. U.S. efforts to interrupt the flow of international financing for North Korea's nuclear operations begun five years ago were also unsuccessful. Georgetown University professor Victor Cha says there's not much the U.S. or other Western countries can do to persuade North Korea to stop. He says there's only one country with any influence.

VICTOR CHA: The Chinese have a wealth of relationships with the North. Some of them public in terms of publicly reported trade figures. And some of them not so public that they can use to put leverage on the North Koreans to try to bring them back to the talks and to get them to stop these missile tests and these nuclear tests.

China's leadership today issued a rare criticism of North Korea, saying Beijing was "resolutely opposed" to nuclear testing. Professor Cha says the U.S. willingness to meet with Pyongyang's leaders means China can no longer blame the U.S. for provoking North Korea. And he hopes that will persuade China to put more backbone into future international sanctions.

In Washington, I'm John Dimsdale for Marketplace.