South Korea detected traces of Xenon, a chemical element usually found near recent nuclear activities, in the country's atmosphere in June, but it does not seem to have originated from North Korea, government sources said Tuesday.

According to the sources, the Korea Institute of Nuclear Safety detected traces of the colorless, odorless noble gas on three occasions in June. Xenon is detected in trace amounts after nuclear bomb tests or other nuclear activities.

After the findings, the government tried to track down its source, but found no signs of nearby nuclear activities in the preceding weeks, the sources said.

The government could not determine the origin of the Xenon gas, one of the sources said, adding that the North may not be responsible because no signs of nuclear activities have been seen in the country at around that time.

Xenon takes about 12 days to reduce by half in the air and North Korea showed no signs of nuclear generation or arms tests in the cited period before the detection, including in its nuclear generation complex in Yongbyon, the source said.

Another source said that the government received no intelligence about the North's nuclear activities in relation with the Xenon detection.

In April, North Korea announced that its nuclear scientists will begin work "readjusting and restarting" a uranium enrichment plant and a graphite-moderated, 5-megawatt reactor in the Yongbyon complex.

The South, however, has not detected any actions by the North to resume the operations of the nuclear reactor, according to the sources. (Yonhap News)