SEOUL—North Korea said it successfully staged its first test of a more powerful form of nuclear weapon, expanding the U.S.’s foreign-policy challenges and highlighting the limits of China’s ability to rein in its volatile ally.
North Korean state television said in a midday broadcast that scientists had successfully detonated a hydrogen bomb at around 10 a.m. local time.
The U.S. Geological Survey reported that it detected a magnitude 5.1 earthquake at that time near North Korea’s nuclear test site in the country’s northeast.
Experts have said it was unclear whether North Korea had developed the ability to build a hydrogen bomb. The magnitude of the latest explosion was the same as a 2013 test of an atomic bomb.
State Department spokesman John Kirby said the U.S. couldn’t confirm North Korea’s claims of a nuclear test but is monitoring the situation.
“We are aware of seismic activity on the Korean Peninsula in the vicinity of a known North Korean nuclear test site and have seen Pyongyang’s claims of a nuclear test,” Mr. Kirby said.