Japan's Prime Minister Shinzo Abe told reporters Friday that "there is a possibility that North Korea has forced a nuclear test," citing the temblor showing wave patterns from a non-seismic source, AP reported.
He says: "If North Korea did conduct a nuclear test, it is absolutely not acceptable, and we must lodge a strong protest."
Japan's Foreign Minister Fumio Kishida also confirmed that Japan Meteorological Agency has detected shaking patterns that are not from a naturally occurred earthquake.
The meteorological agency detected a magnitude 5.3 shaking in North Korea, near the country's nulear test facility.
NHK says Japan's Nuclear Regulation Authority is now analyzing radiation levels at monitoring stations nationwide to see if there is any change.