South Korean media reports said Sunday that North Korea has been digging tunnels at a nuclear test site, sparking concerns that it could be preparing for another nuclear test.
Quoting government and military sources, the Yonhap news agency said the North has started building at least two new tunnels at Punggye-ri in the northeastern province of North Hamgyong.
North Korea conducted its two previous plutonium-fueled nuclear tests in 2006 and 2009 at the site.
Yonhap quoted an unidentified official as saying Pyongyang would probably conduct a third test using its available supply of plutonium, which is estimated to be enough for six to eight bombs.