The U.S. State Department says it has yet to confirm whether North Korea conducted a nuclear test on Monday.

AFP news agency quoted department spokesman Andy Laine as saying that Washington has seen reports of the nuclear test, but cannot yet confirm them. He said the department is still gathering related data.

North Korea said it conducted an underground nuclear test Monday morning to "bolster its nuclear deterrent for self-defense."

South Korean intelligence detected a magnitude four-point-five earthquake near the North Korean town of Punggye in Gilju County, North Hamgyeong Province, at 9:54 a.m.