The epicenter is marked in red. Captured from Google Map

By Park Si-soo

A moderate 2.1-magnitude earth tremor was detected in North Korea's mining town of Pyonggang around noon Thursday.

The Korean Meteorological Administration (KMA) said it was "artificial" seismic activity, presumed to be the result of an explosion inside a mine.

"The epicenter is measured to be near the land surface," a KMA official said.

It took place two days after South Korea's spy agency revealed North Korea was rebuilding part of a dismantled long-range missile test launch site in Sohae.

U.S. President Donald Trump said Wednesday he would be "disappointed" if the report is true.