Obama vows U.S. action on North Korea

Obama must now decide how to mix what he called "stronger international pressure" with a new set of diplomatic overtures, at a moment when, his aides are acutely aware, Iran and other nations are taking his measure, examining the confrontation with North Korea for hints of how he will handle complex confrontations to come.

It will take days, or weeks, of testing radioactive particles vented into the atmosphere to calculate the size of the device detonated Monday, and even then, there will be continuing debate about whether North Korea has the engineering capability to make a weapon compact enough to fit in the warhead of a missile, much less to deliver it to a target.

Japanese and South Korean officials acknowledged they are less concerned about direct attack from North Korea — which would almost certainly result in a devastating, U.S.-led response — than North Korea playing its last card: Selling its twice-tested nuclear-weapons technology on the black market, much as it has sold its missile and reactor technology in the Middle East.

"We're back to the same problem Bush had," said one exasperated intelligence official. "The threat is not that they will shoot off a nuclear weapon, it's that they will sell nuclear material."

In emergency conference calls just after the North gave less than an hour's notice through its mission to the United Nations that it was about to conduct a test early Monday, Obama's team came to some preliminary strategies.

One senior administration official said that the United States would never grant full diplomatic recognition to North Korea — or sign a peace treaty formally ending the Korean war — unless its nuclear capability is dismantled.

To devise a common response, administration officials began planning a series of trips to meet with Asian leaders, and eventually with the central player in the diplomatic drama: China. Defense Secretary Robert M. Gates will begin the effort this week on a previously scheduled trip for an annual defense meeting. His spokesman, Geoff Morrell, said, "There is simply no greater security challenge facing Asia than a nuclear-armed North Korea," and Gates plans to work "to figure out how we collectively can prevent that from becoming a reality."

Contributing: William J. Broad, Thom Shanker, Mark Landler and Neil MacFarquhar, New York Times News Service; Hyung-Jin Kim, Associated Press