UPI is reporting that a 2.6-magnitude earthquake struck an area of North Korea where Pyongyang has been carrying out its underground nuclear tests.

South Korea’s meteorological agency said Tuesday the earthquake originated from an area about 30 miles north-northwest of Kilju, North Hamgyong Province, and is likely to have been triggered by North Korea’s sixth nuclear test conducted September 3, 2017, News 1 reported.

South Korean news reports say that the underground tests at Kilju have caused cave-ins and released nuclear contamination at the mountainous facility. There are also unconfirmed reports of worker deaths and radiation sickness in nearby communities.