SEOUL, South Korea (AP) – South Korea’s Yonhap news agency says Seoul believes North Korea has conducted its fifth nuclear test explosion.

The agency’s report cited an unidentified government official. South Korea’s Defense Ministry couldn’t immediately confirm the report.

Monitors earlier Friday reported an earthquake near North Korea’s northeastern nuclear test site, a strong indication of a nuclear test.

South Korea’s Joint Chiefs of Staff said in a statement that “artificial seismic waves” from a quake measuring 5.0 were detected near the Punggye-ri test site, and officials were analyzing whether it was a nuclear test.

North Korea conducted its fourth nuclear test earlier this year, part of its push for a nuclear-armed missile that could one day reach the U.S. mainland.