North Korea has started digging tunnels at its nuclear test site in apparent preparation for a third atomic detonation, a report said Sunday.
North Korea started building at least two new tunnels at its Punggye-ri facility in northeastern North Hamgyong province for a possible underground atomic test, according to a South Korean official.
The source told Yonhap news agency: "It is obvious evidence that it (the North) is preparing a third nuclear test."
The report comes after Pyongyang racked up tensions at the end of last year by launching an artillery barrage against a South Korean island and disclosing a new nuclear programme, before going on a charm offensive last month.
Pyongyang is building more than one tunnel to choose the best one for a possible test, as tunnels cannot be reused after a nuclear test blast, the official claimed.
The official added the possible test would probably be carried out using material from the North's plutonium stockpile, which Seoul and Washington estimate to be enough for six to eight bombs.
Cross-border ties have been icy since Seoul last May accused Pyongyang of sinking a South Korean warship and killing 46 sailors – a charge the North angrily denied.
The tension soared further when Pyongyang's shelling of a frontier island of Yeonpyeong left four South Koreans, including two civilians, dead in November.
The first cross-border meeting since the shelling, held earlier this month, broke down as Pyongyang officials stormed out after Seoul demanded an apology for the Yeonpyeong bombardment and the sinking of the warship.
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