At least four North Korean defectors have shown symptoms consistent with radiation exposure, including chromosomal abnormalities, South Korea’s Unification Ministry said Wednesday.

The four defectors were among a group of 30 refugees who agreed to be tested, out of a total of 114 defectors from the region near North Korea’s Punggye-ri nuclear site.

All 30 hail from the North Korean region of Kilju, where the country has conducted six underground nuclear bomb tests since 2006. All of those tested fled North Korea before the country’s fourth nuclear test in January 2016.

Ministry officials who spoke with South Korea’s Yonhap News Agency cautioned that the tests, while indicative of radiation exposure, weren’t necessarily definitive. Other environmental factors like age and smoking could also cause similar damage.

“The possibility of radiation exposure can be suspected,” the unnamed official said, “but it has not been verified whether nuclear tests affected the person as there is a lack of information assessing living environments in North Korea.”

North Korean soldiers attend a mass rally in Pyongyang to celebrate North Korea's declaration on Nov. 29 it had achieved full nuclear statehood. (Photo: KIM WON-JIN via Getty Images)

The accounts nonetheless align with anecdotal tales from Kilju defectors, who described a heavily contaminated region in interviews with The Research Association of Vision of North Korea earlier this year.

Residents in the area told the group that after the sixth nuclear test, some 80 percent of the trees planted in the area have died, underground wells have dried up and babies have been born with health defects.

That’s consistent with what could be expected from repeated underground nuclear explosions, Suh Kyun-ryul, a professor of nuclear engineering at Seoul National University, told the South Korean newspaper Chosun Ilbo.

“Due to the collapsed ground layer, fissures must have formed underneath, leading to contamination of the underground layer and water supply.”

After North Korea’s sixth and largest nuclear test on Sept. 3, unnamed sources told the Japanese TV broadcaster Asahi a collapsed tunnel at the Punggye-ri site potentially killed as many as 200 people.

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