From Seoul to Washington, Beijing to the United Nations, world powers are looking at ways to punish Pyongyang for the test of what it called a new and powerful hydrogen bomb.
The South's propaganda broadcasts, which will start Friday, will infuriate authoritarian Pyongyang because they are meant to raise questions in North Korean minds about the infallibility of the ruling Kim family.
Experts, meanwhile, are trying to uncover more details about the detonation that drew worldwide skepticism and condemnation.
It may take weeks or longer to confirm or refute the North's claim that it successfully tested a hydrogen bomb, which would mark a major and unanticipated advance for its still-limited nuclear arsenal.
Even a test of an atomic bomb, a less sophisticated and less powerful weapon, would push its scientists and engineers closer to their goal of building a nuclear warhead small enough to place on a missile that can reach the US mainland.
The statements said the countries "agreed to work together to forge a united and strong international response to North Korea's latest reckless behavior."
Obama also reaffirmed the "unshakeable US commitment" to the security of South Korea and Japan, according to the statements.
South Korean and US military leaders also discussed the deployment of US "strategic assets" in the wake of the North's test, Seoul's Defense Ministry said Thursday.
Ministry officials refused to elaborate about what US military assets were under consideration, but they likely refer to B-52 bombers, F-22 stealth fighters and nuclear-powered submarines.
