NEW YORK — (CNN) Following North Korea’s purportedly successful H-bomb test Wednesday, the United States, South Korea, Japan and China are all testing for airborne or ground radiation in the region, but so far attempts to verify the magnitude of the test have turned up nothing.

Over 24 hours after North Korea announced a successful test, South Korean and Japanese attempts have not reported finding any evidence of radiation.

The Japanese Nuclear Regulation Authority, which is strengthening its monitoring activities, and the Japan Chemical Analysis Center, which is analyzing dust samples collected by the country’s Air Self Defense Force, said “there was no particular change” in environmental radiation levels, a finding echoed by South Korean monitors.

China’s Ministry of Environmental Protection, which was monitoring soil samples near its border with the North, also reported no changed in radiation levels early Thursday.

According to Norsar, a Norway-based group that monitors nuclear tests, this test took place deeper underground, so it would be harder to monitor radiation and thus determine the type of weapon tested.

The group added that, based on the seismic readings, the blast which caused a magnitude 5.1 seismic event, was equivalent to less than 10,000 tons of TNT, smaller than those of the atomic bombs used on Hiroshima and Nagasaki, and far less than thermonuclear weapons that typically are as potent as millions of tons of TNT.

The underground test, which happened at 10 a.m. (8:30 p.m. ET Tuesday), corresponded with a magnitude-5.1 seismic event centered 12 miles (19 kilometers) east-southeast of Sungjibaegam, according to the U.S. Geological Survey.

U.N. pursues punitive measures

The U.N. Security Council is set to implement “significant” punitive measures after North Korea’s nuclear test and will begin working on a new resolution “immediately,” a statement released by Security Council President Elbio Rosselli says.

After Wednesday’s meeting, the council, which includes China, Russia and the United States, together condemned the test as a “clear violation of (past) resolutions … and of the nonproliferation regime.”

Past U.N. measures included arms, nonproliferation and luxury good embargoes, a freeze on overseas financial assets and a travel ban. None of them have so far stopped North Korea from continuing its nuclear program.

Meanwhile, U.S. President Barack Obama spoke to the leaders of South Korea and Japan, who both joined the President in condemning the act. Obama reaffirmed the United States’ defense commitments to both of its regional allies.

South Korean President Park Geun-hye’s office added that the two leaders agreed “there should be a corresponding price for this nuclear test.”

South Korea will also resume propaganda broadcasts into North Korea, the presidential Blue House announced. In August tensions escalated following a series of broadcasts from near the South Korean side of the Demilitarized Zone (DMZ).

Claims analyzed

North Korea bragged Wednesday about the “spectacular success” of its first hydrogen bomb test, a defiant act that leader Kim Jong Un, in a statement read on state television, said would “make the world … look up to our strong nuclear country.”

However, White House spokesman Josh Earnest said, “The initial analysis is not consistent with the North Korean claims.”

If it was, it would be a game changer, said Mike Chinoy, a fellow at the University of Southern California’s U.S.-China Institute.

“But evidence seems to suggest it wasn’t a full hydrogen bomb.”

However, he said that with each test North Korean nuclear scientists get more data and as a result closer to being able to miniaturize nuclear weapons, a development that would allow the country to deploy nuclear weapons on long-range missiles.

“Whether it was a full H-bomb or not it is still a worrying development,” he said.

‘Boosted’ fission weapon?

It’s possible North Korea has a “boosted” weapon, one that uses a small amount of fusion to boost the fission process, but is not a hydrogen bomb.

Indeed, given the secrecy surrounding North Korea, it may be difficult to ever know; the last test, in 2013, has experts split over whether the device detonated then was plutonium or uranium.

Even if it wasn’t an H-bomb, there’s little doubt that North Korea did conduct a new significant nuclear test despite persistent calls not to do so.

Ongoing analysis

“We won’t know for another few days or weeks whether this was (a hydrogen bomb),” said Martin Navias, a military expert at King’s College London. “It doesn’t look like one; … one would have expected it to be greater if it was an H-bomb.”

After being briefed by his nation’s military, South Korean lawmaker Shin Kyung-min questioned the credibility of the hydrogen bomb claim. Joo Ho-young, who heard from the nation’s intelligence service, told reporters, “It could be different from a usual hydrogen bomb.”

Count Bruce Bennett, a senior defense analyst at the nonpartisan Rand research group, among the skeptics. He said North Korea has had trouble “mastering even the basics of a fission weapon,” so it’s a big leap to think it could create an even more complicated hydrogen bomb.

And that — sticking it to world and regional powers — may be Pyongyang’s aim.

“The present-day grim reality clearly proves once again the immutable truth that one’s destiny should be defended by one’s own efforts,” North Korea’s official KCNA news agency reported. “… The army and people of the DPRK will steadily escalate its nuclear deterrence of justice both in quality and quantity to reliably guarantee the future of the revolutionary cause.”

China spoke out strongly against the latest test, saying it had no notice.

The anger and danger were felt most in South Korea, which was split from the North seven decades ago.

A heavily militarized state

North Korea’s conventional weaponry is dated, with limited effectiveness. That’s one reason, experts speculate, Pyongyang has sought nuclear weapons: to project power internationally.

Combined with its secrecy and seclusion, North Korea’s us-against-the-world perspective and the fact it doesn’t play by traditional rules make it unpredictable at best and dangerous at worst. Add nuclear weapons to the mix — even if they aren’t thermonuclear — and Pyongyang could unleash devastation of a sort not seen in over 70 years.

While it has done little outwardly to develop its economy, North Korea has put a lot of focus on its military, carrying a huge standing army of 1.2 million active soldiers plus 7.7 million reservists in a country of 25 million people.

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