The State Department in a report last week expressed concerns that "it is assessed that the results of the detonations at [the Punggye-ri] nuclear test site on May 24, 2018, are almost certainly reversible."

North Korea could restore a blown-up nuclear test site to its original state or simply develop a new one, a U.S. State Department report has warned.

"It is possible that North Korea could develop another nuclear test site if it chose to do so," the report adds.

"This, combined with North Korea's failure to permit qualified international inspectors to observe and verify the dismantlement, calls into question North Korea’s long-term commitment to forego further nuclear explosive tests and the broader denuclearization process," it warned.

In May last year, right before the first U.S.-North Korea summit, the North allowed reporters to observe the blowup of the test site from a distance but refused to let inspectors verify the event.

The U.S. also worries about the possibility of Chinese cooperation in the North's missile development. The report noted that Chinese entities continued to supply good banned under the Missile Technology Control Regime to the North, Iran, Syria, and Pakistan in 2018.

"Although the United States has asked that China investigate and put a stop to such activities, most of these cases remain unresolved," it added.