The government has beefed up monitoring of North Korea's nuclear activities given the rising possibility of Pyongyang conducting an underground nuclear test.

A government source said Sunday that the heightened surveillance is being conducted via the Korea Institute of Geoscience and Mineral Resources, an office under the Science and Technology Ministry.

Six military officials have also gone to the institute in an unprecedented move to conduct round-the-clock surveillance.

Under the Comprehensive Test Ban Treaty, the institute is monitoring the North via the Korea Society of Remote Sensing, which is registered as a nuclear experiment observatory.

Reports say several observatories have been set up along the Demilitarized Zone to track the North's nuclear activities.

The day after Pyongyang test-fired missiles on July 5th, a spokesman for the North Korean Foreign Ministry warned of stronger physical measures if the North is provoked over its missile tests.