"The republic's first hydrogen bomb test has been successfully performed at 10:00 a.m. on Jan. 6, 2016, based on the strategic determination of the Workers' Party," a state television news reader announced, according to AFP.
"If there's no invasion on our sovereignty we will not use nuclear weapon," North Korea’s state news agency said, according to CNN.
"This H-bomb test brings us to a higher level of nuclear power."
A spokesman for the U.S. Pacific Command told CNN that the United States is aware of the seismic activity.
"We remain vigilant and are fully committed to working closely with our Republic of Korea ally to maintain security on the peninsula," the spokesman said.
South Korea’s Foreign Ministry told CNN it is holding an emergency meeting following the seismic activity.
Some took to social media to express skepticism of the legitimacy of North Korea’s claim.
The news came shortly after South Korean officials reported an “artificial earthquake” in North Korea.
An official from South Korea’s weather agency said the earthquake occurred about 30 miles north of where North Korea’s main nuclear testing site is located.
The U.S. Geological Survey said on its website that it measured the magnitude of the “artificial earthquake” at 5.1.
The last time North Korea conducted a nuclear test was in February 2013.
The White House said that it was aware of North Korea’s claims but could not confirm them.
“We are monitoring and continuing to assess the situation in close coordination with our regional partners,” National Security Council spokesman Ned Price said in a statement.
“North Korea conducted its first nuclear test in 2006 and, until today, has done so twice since, but we have consistently made clear that we will not accept it as a nuclear state,” Price added. “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.”
Pyongyang first claimed to have developed a thermonuclear weapon in December, but outside analysts were largely skeptical at the time.
If confirmed, the North Korean test would be a dramatic increase in the hermit nation’s nuclear capabilities.
Commonly referred to as hydrogen bombs, weapons that use nuclear fusion as well as fission can be 10 to 100 times more powerful than the initial generation of atomic weapons, such as those that were dropped by the U.S. over Japan during World War II.
The test would also escalate the stakes in one front of the Obama effort to limit the spread of nuclear weapons after the significant achievement last year of an agreement designed to halt Iran from acquiring a nuclear weapon.