US intelligence: 'Highly probable' North Korea tested hydrogen bomb The bomb had an explosive yield of 140 kilotons, intelligence indicates.

 -- U.S. intelligence has assessed that it is “highly probable” that North Korea detonated a hydrogen bomb last weekend as it has claimed, according to a U.S. official.

The blast was also assessed to have had an explosive yield of more than 140 kilotons, higher than initially believed, making it nearly 10 times as powerful as the atomic bomb dropped by the United States on Hiroshima in World War II.

As U.S. intelligence continues to assess the underground nuclear test the official cautioned there is a chance that waht North Korea tested may have been a fission bomb bolstered to convert it into a thermonuclear bomb, though not necessarily a Hydrogen bomb.

Hydrogen bombs have exponentially more explosive power than atomic bombs, which North Korea has previously tested.

The U.S. Geological Survey measured the North Korean blast as being equal to an earthquake with a 6.3 magnitude.

North Korea sparked international condemnation following its sixth underground nuclear test.

"Military action is certainly an option," said President Donald Trump on Thursday at a White House news conference. "Hopefully we won't have to use it on North Korea."

He added: "I can tell you that North Korea is behaving badly and it has to stop."

Following the blast, a U.S. intelligence official had described the U.S. as "highly confident" that North Korea had tested "an advanced nuclear device" that was not inconsistent with North Korea’s claims.

Afterward, some other officials advanced that further, saying intelligence assessments determined it was "possible" that North Korea had tested a hydrogen bomb.

On Thursday, an Air Force WC-135 “Constant Phoenix” monitoring aircraft flew from Kadena Air Force Base in Okinawa to detect any radioactive isotopes that may have made it into the atmosphere.