The government has confirmed that no radioactive contamination has reached the South following North Korea's underground nuclear test earlier this month.

The Ministry of Science and Technology said Tuesday that radiation levels were normal around ten to 20 micro Roentgens per hour based on analysis of air samples collected from 38 monitoring centers and mobile radiation detectors.

Although a trace of radioactive xenon was found in an air sample taken from the northern part of the East Sea, it is only three-millionths of the yearly allowable level and will have little impact on people or the environment.

Meanwhile, the United States said that, considering the amount of radioactive krypton found around the North, it suspected Pyongyang may have used plutonium for its nuclear test.