South Korean and U.S. intelligence authorities say they have yet to detect any radioactive substances that would indicate North Korea successfully detonated a nuclear device late last month.

An official at the Korea Institute of Nuclear Safety said it is currently analyzing the components of air samples collected in the sky over the East Sea. But as of now, no radioactive substances have been found in the analysis.

The aerial existence of radioactive substances, like krypton and xenon, is crucial in determining whether a nuclear test took place.

The United States also says that a U.S. reconnaissance aircraft has not found any radioactive substances in its air samples collected over the East Sea.