North Korea Claims Successful H-Bomb Test

North Korea said Wednesday it had conducted a hydrogen bomb test, a defiant and surprising move that, if confirmed, would put Pyongyang a big step closer to improving its still-limited nuclear arsenal.

A television anchor read a typically propaganda-heavy statement on state TV saying North Korea had tested a "miniaturized" hydrogen bomb, elevating the country's "nuclear might to the next level" and providing it with a weapon to defend itself against the United States and its other enemies.

The statement said the test was a "perfect success."

Pyongyang also claimed the test was "conducted in a safe and perfect manner" and "had no adverse impact on the ecological environment."

Crowds dressed in thick winter coats gathered outside a large video screen near a Pyongyang train station to cheer and take video and photos on their mobile phones as the state TV anchor, dressed in a pink traditional Korean hanbok, delivered the statement.

North Koreans react as they watch a news broadcast on a video screen outside Pyongyang Railway Station in Pyongyang

South Korean president Park Geun-hye convened an emergency meeting of the country's national security council, ordered her military to bolster its combined defense posture with U.S. forces, and called the test a "grave provocation" and "an act that threatens our lives and future." Japanese Prime Minister Shinzo Abe said, "We absolutely cannot allow this." China called the test "highly regrettable."

U.S. officials were "looking into" the event, CBS News correspondent David Martin reported.

"While we cannot confirm these claims at this time, we condemn any violation of UNSC Resolutions and again call on North Korea to abide by its international obligations and commitments," National Security Council spokesman Ned Price said.

"We will continue to protect and defend our allies in the region, including the Republic of Korea, and will respond appropriately to any and all North Korean provocations," Price said.

However, Seoul's intelligence agency said the device may not have been a hydrogen bomb, South Korea's Yonhap News Agency reported, according to the Reuters news agency. South Korea's meteorological agency said it hadn't detected any radiation after the supposed test, Reuters added. And South Korea's vice defense minister said it was difficult to believe the device was a hydrogen bomb, Yonhap said, again according to Reuters.

Japan's government also said its environmental detectors noted no radiation after the claimed test.

The Associated Press contributed to this report.