North Korea has been digging special tunnels at a nuclear test site in Punggye-ri in North Hamgyong Province, sparking concerns that it may be preparing for another nuclear test, government and military sources said Sunday.

North Korea conducted its two previous plutonium-fueled nuclear tests, one each in 2006 and 2009, at the site.

“South Korea and U.S. intelligence authorities have spotted the North building a couple of additional tunnels in Punggye-ri,” said a government source. “It’s obvious that North Korea is preparing for a third nuclear test.”

Reports have emerged about signs that the reclusive regime may be preparing for its third nuclear test at the Punggye-ri nuclear test site in northeastern North Korea.

The source gave no further details on how many tunnels Pyongyang has constructed.

“Underground bases can’t be reused after a nuclear test blast,” he said, adding that Pyongyang is building more than one tunnel so that it can choose the best one for the atomic test.

“It’s unclear whether the North will conduct a plutonium-fueled nuclear test or uranium-fueled one,” the source said. “But it’s likely to opt for the plutonium-based program as it has already revealed the existence of a modern uranium enrichment facility and expects strong opposition from China.”

North Korea revealed in November that it was running a uranium enrichment facility. Pyongyang claims the uranium enrichment program is for peaceful energy development, but outside experts believe it could give the country a new source of fission material to make atomic bombs in addition to its known plutonium-based nuclear weapons program.

Meanwhile, the South Korean military is keeping tabs on the movements to check whether the North will conduct nuclear tests and long-range missile tests at the same time.

Reports said that North Korea has completed the construction of a new sophisticated missile launch site on its western coast near the Chinese border in an apparent bid to test-fire another ballistic missile that can reach the mainland U.S.

North Korea has conducted long-range missile tests three times

― in 1998, 2006 and 2009 ― which were seen as partial successes.

“The Joint Chiefs of Staff is mapping out programs to deal with the North’s third nuclear test, long-range missile launch and hovercraft attacks,” said a military source.

“We are closely watching its new missile launch site in Dongchang-ri and the Punggye-ri nuclear test site.”

He said that the Dongchang-ri missile site is not yet completed, while construction of a naval base that can accommodate 70 hovercrafts in Koampo, Hwanghae Province, will be finished soon.

Inter-Korean tensions have escalated since North Korea launched an unprovoked artillery attack on the South’s Yeonpyeong Island in November, killing two civilians and two marines. The bombardment came eight months after a North Korean torpedo sank a South Korean warship and killed 46 sailors.

The North had offered talks earlier this month, but the first inter-Korean contact since the Yeonpyeong bombardment collapsed as the two sides failed to agree on the agenda and other procedural issues for a higher-level meeting to reduce tensions on the Korean Peninsula.

The two Koreas are still technically at war after the 1950-53 Korean War ended in a truce, not a peace treaty. About 28,500 American troops are stationed in South Korea to deter threats from North Korea. 

(Yonhap News)