A higher than average level of the radioactive material xenon was detected last month east of the inter-Korean border.

The gaseous element was discovered by the northernmost detection station managed by the Korea Institute of Nuclear Safety.

Xenon-135 (Xe-135) and krypton-85 (Kr-85) are gaseous radioactive isotopes and their detection is typically regarded as evidence of a nuclear experiment.

North Korea last month declared it had successfully conducted a nuclear fusion reaction using its own technology. Based on the detection of xenon, some experts speculate that North Korea may have developed the core technology to produce hydrogen bombs, which are more powerful than uranium- and plutonium-based nuclear weapons.

A presidential official told Seoul-based Yonhap News that although xenon was detected, no seismic waves were observed. Based on circumstantial evidence, the official concluded that no nuclear test was conducted.