North Korea on Sunday conducted its sixth and most powerful nuclear test, which it claimed was an advanced hydrogen bomb designed for a long-range missile.

Outside observers haven’t verified that the weapon was a hydrogen bomb, but experts widely agree that the weapon created an explosion that far exceeded previous North Korean nuclear tests.

Norsar, a Norwegian geoscience research foundation, said in a news release that it estimated the explosive yield of the recently tested bomb to be at 120 kilotons TNT. In other words, its power equaled or exceeded 264.55 million pounds worth of TNT.

“North Korea claims that this was a test of a hydrogen bomb; the same claim was made for previous tests,” Norsar said. “It is not possible from the seismic data alone to determine if this was a test of a hydrogen bomb, but we can say in general that the credibility of the claim increases with increasing explosive yield.”

By comparison, the “Little Boy” atomic bomb dropped on Hiroshima during World War II yielded roughly 15 kilotons TNT. The “Fat Man” bomb dropped on Nagasaki was about 20 kilotons TNT.

The most powerful nuclear weapon ever tested, meanwhile, is said to be a Soviet hydrogen bomb that yielded 50,000 kilotons TNT.

—Reuters contributed to this report.