SEOUL, South Korea: North Korea said Wednesday it had conducted a powerful hydrogen bomb test, a defiant and surprising move that, if confirmed, would be a huge jump in Pyongyang’s quest to improve its still-limited nuclear arsenal.

A television anchor said in a typically propaganda-heavy statement that the North had tested a “miniaturized” hydrogen bomb, elevating the country’s “nuclear might to the next level” and providing it with a weapon to defend against the United States and its other enemies.

The statement said the test was a “perfect success,” and the announcement was celebrated on the streets of Pyongyang.

South Korean President Park Geun-hye ordered her military to bolster its combined defense posture with US forces and called the test a “grave provocation” and “an act that threatens our lives and future.”

Strong condemnation of the announced test rolled in from around the world, including from Lassina Zerbo, the head of the Vienna-based CTBTO, which has a worldwide network of monitoring stations to detect nuclear testing. Zerbo told AP by phone, “This is indeed a wakeup call ... and I am convinced it will have repercussions on North Korea and international peace and stability.”

US House Speaker Paul Ryan said that North Korea’s reported nuclear bomb test appeared to be a provocation but that it was too soon to push for a US response until the facts of the incident are known.

“I think this means we have to have a well-honed response with our allies on this rogue regime,” Ryan told reporters at a news conference after a meeting of his Republican Party.

“We don’t know that he facts yet,” he said, adding: “This looks like a provocation.”

Meanwhile, US Republican presidential candidate Donald Trump said on Wednesday that China should take the lead in tackling North Korea.

“China has total control,” Trump said on Fox News. “They have total control over North Korea, and China should solve that problem. And if they don’t solve the problem, we should make trade very difficult for China.” The UN Security Council tentatively set an emergency meeting on Wednesday to discuss the surprise move.

There has long been skepticism by Washington and nuclear experts about past North Korean claims about H-bombs, which are much more powerful, and much more difficult to make, than atomic bombs. A confirmed test, however, would be seen as extremely worrying and lead to a strong push for new, tougher sanctions on North Korea at the United Nations, which quickly announced an emergency Security Council meeting on North Korea. It would also further worsen already abysmal relations between Pyongyang and its neighbors.

North Korean nuclear tests catch global attention because each new blast is seen as pushing North Korea’s scientists and engineers closer to their goal of building a bomb small enough to place on a missile that can reach the US mainland.

One expert in Seoul said the 5.1 magnitude of the quake set off by Wednesday’s test was likely too small to be an H-bomb test. However, the North could have experimented with a “boosted” bomb that uses some nuclear fusion fuel along with more conventional uranium or plutonium fuel, said Jaiki Lee, a professor of nuclear engineering at Seoul’s Hanyang University.

In Pyongyang, meanwhile, the announcement was greeted with an expected rush of nationalistic pride, and some bewilderment.

A large crowd gathered in front of the city’s main train station to watch the special bulletin announcing the news of the test on a big screen in the station’s plaza. Some took videos or photos of the screen on their mobile phones. Others applauded and cheered as the TV announcer, wearing a pink traditional Korean gown, announced the news.

One of the people in the plaza, Kim Sok Chol, 32, told The Associated Press that he doesn’t know much about H-bombs, but added that “Since we have it the US will not attack us.”

University student Ri Sol Yong, 22, said, “If we didn’t have powerful nuclear weapons, we would already have been turned into the slaves of the US“

Just how big a threat North Korea’s nuclear program currently poses to the outside world is something of a mystery. North Korea is thought to have a handful of rudimentary nuclear bombs and has spent decades trying to perfect a multistage, long-range missile to eventually carry smaller versions of those bombs.

Some analysts say the North hasn’t likely achieved the technology needed to manufacture a miniaturized warhead that could fit on a long-range missile capable of hitting the US mainland. But there is a growing debate on just how far the North has advanced in its secretive nuclear and missile programs.

North Korea needs nuclear tests for practical military reasons.