Pictures from inside a tunnel at North Korea's nuclear testing ground in the far northern part of the country have been revealed for the first time.

The photographs,.. captured by South Korea's defense ministry, show a horizontal tunnel with three traps and 10 doors, including an entrance, likely designed to prevent radioactive material and debris from making their way outside after a nuclear test.

In fact, the western tunnel, which is less than 1-kilometer-long and spirals in parts, helped Pyongyang secretly conduct its second test in 2009.

The stills were captured from a video aired on the North's state-run television station in 2010, and Pyongyang said the video was recorded during its second nuclear test the previous year.

Citing an official on Monday, Seoul's Yonhap News says high-level officials from the North Korean regime have recently visited the western tunnel, likely to run through a final check of test preprarations.

With the clock ticking on a third nuclear test, top nuclear envoys from South Korea and China met in Beijing on Monday to seek out ways to stop it.

The South Korean negotiator urged China to keep up the diplomatic pressure on its long-time ally.

Lim also told his Chinese counterpart Wu Dawei if North Korea launches another provocation, Seoul, Beijing, Washington and allies should work together to penalize the North.

In Seoul, the South's Unification Minister told lawmakers that it's highly likely Pyongyang will in fact test its nuclear capability, and said he believes the North could carry out an enriched uranium-based test this time around.

Choi You-sun, Arirang News.

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