The Democratic People's Republic of Korea (DPRK) may have had a failed test of some components of a hydrogen bomb earlier this month, CNN reported on Thursday, citing a US official.
"There may have been a partial, failed test of some type of components associated with a hydrogen bomb," a US official familiar with the latest US assessment told CNN.
The official said that the assessment was based on "careful examination of latest intelligence analysis of the test data."
However, there is no final conclusion, said the official.
Although the US still denies that DPRK tested a hydrogen bomb, "air sampling conducted after the test has proved inconclusive", which prompted Washington to review the seismic data, the official added.
Pyongyang tested a nuclear device on Jan 6 that DPRK said was a hydrogen bomb.
The official said that the analysis showed that the test was conducted more than two times deeper underground than originally assessed - at a depth consistent with what might be needed for a hydrogen bomb.
However, the size of the seismic event and other intelligence indicates it was not likely a fully functioning device. The official said that it is possible Pyongyang believed it conducted a full hydrogen bomb test, but the US thinks it was likely only some components that exploded.
US State Department spokesman Mark Toner told reporters earlier on Thursday that the US still believes that Pyongyang did not test a hydrogen bomb.