http://www.defensetech.org/archives/003143.html
In early December 2006, intelligence sources indicated activities were underway at the Mount Mant’ap nuclear test site near the village of Punggye-ri in North Hamgyŏng Province. The activities were first disclosed by South Korean National Assemblyman Chŏng Hyŏng-gŭn of the Grand National Party (GNP or “Hannaradang”) on December 21. Chŏng’s disclosure followed South Korean Defense Minister Kim Chang-su’s December 15th admonition to 30 senior military commanders “to be thoroughly prepared to counter the possibility of a second or third nuclear test by North Korea.” According to National Assemblyman Chong, North Korea had prepared two tunnels under Mount Mant’ap, and the October 9, 2006 test was conducted in a tunnel on the eastern side of the mountain while recent activities have been at the western tunnel. According to a South Korean government source, the movement of people and vehicles has been detected at the site, and the activities are similar to those that preceded the first test.