South Korea's nuclear safety agency said it found traces of xenon gas in the environment nearly a week after North Korea conducted its latest nuclear test.

The Nuclear Safety and Security Commission discovered trace amounts of the radionuclide after analyzing samples collected from the air, ground and water, according to Yonhap News Agency.

Ignoring international outcry, North Korea conducted its sixth nuclear test Sunday after allegedly detonating a hydrogen bomb that can be fitted on top of an intercontinental ballistic missile.

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South Korean Prime Minister Lee Nak-yon said Thursday he expects its neighbor to launch a missile Saturday while celebrating its founding day. North Korea has already fired 21 missiles this year.

The xenon gas inflow is still being studied to determine if it came from North Korea's nuclear test, South Korea's safety agency said.

The agency added the level of radioactive material detected in the analysis is not enough to cause any health effects.