North Korea is reportedly digging several tunnels at its nuclear test site in Punggye-ri, North Hamgyeong Province.A South Korean government source said on Sunday that intelligence gathered from both Seoul and Washington shows that the North has drilled a number of underground tunnels indicating that the reclusive regime is preparing for another nuclear test.North Korea has already conducted two nuclear tests at the site in 2006 and 2009.The source did not specify the exact number of tunnels but it is estimated to be at least two or three.He added as a tunnel cannot be reused once a nuclear test has been carried out, additional construction means that there is a high chance of a third nuclear test.The source explained it is not known whether Pyeongyang will choose plutonium or uranium, but since it already revealed its uranium enrichment facility last November and considering China's resistance the secretive state is likely to carry out a plutonium-based test.Meanwhile, the South Korean military is keeping a close eye on potential missile attacks from the North along with a nuclear test.A military source says the Joint Chiefs of Staff is planning measures to deal with possible North Korean aggression this year, such as a third nuclear test, a long-range missile launch and hovercraft attacks as well as closely monitoring the missile launch site in Dongchang-ri, as well as the Punggye-ri nuclear test site.Choi Won-young, Arirang News.