Seoul, South Korea (CNN) -- Gen. Hahn Sung-Chu never believed North Korea could dig a tunnel that reached Seoul -- until now. Standing inside a basement of an apartment block in the heart of the capital, the former two-star general in the South Korean military says, "This is a kind of invasion, North Korean soldiers working underneath us." Hahn says residents had complained of underground vibrations, but the subway does not run beneath them. He says dowsers detected three tunnels, 13 to 16 feet (4 to 5 meters) wide at a depth of up to 39 feet (12 meters). His team drilled two bore holes to lower a camera, but before they could, they detected two underground explosions and their drill holes were blocked. Hahn is certain that North Korean soldiers were working beneath their feet, protecting the tunnel.
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Ex-S. Korean general suspects a North Korean tunnel is under a Seoul apartment block
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But S. Korean Defense Ministry believes tunnels can't extend beyond 6 miles from the DMZ
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A defector says tunnel operations peaked in the 1980s
Four tunnels from the @placeholder have been found in all, although none since 1990.