A 4.9-magnitude earthquake was detected Tuesday in a region of North Korea known as the site of its first two underground nuclear bomb tests, stoking concern that the nation may have conducted its anticipated third nuclear test.

The U.S. Geological Survey reported the seismic activity late Monday night EST (11:57 a.m. Korean time), but it has not been confirmed as a nuclear test by either North or South Korean authorities, according to the Associated Press.

However, the office of the South Korean president said it was "likely" a nuclear test, Reuters reported, citing South Korea's Yonhap news agency.

The area where the tremor was felt has no history of earthquakes or other such natural seismic disturbances, CNN reported, which only bolsters the theory that the quake came as the result of a third nuclear test.

North Korea declared last month that it had plans to carry out a third nuclear weapons test as a response to United Nations sanctions that went into effect earlier this winter, according to the AP.

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