By Barbara Starr and Jeremy Herb, CNN
North Korea has recently resumed digging tunnels and construction activities at its underground nuclear test site, according to five US officials. Commercially available satellite imagery had shown some indications of activity on the surface at Pyongyang’s remote Punggye-ri nuclear test site.
It is not yet clear how soon the regime would be capable of testing a device at the site, as it depends on the pace of the activity, the officials say.
The preparations for a possible underground nuclear test come after North Korea tested its first suspected intercontinental ballistic missile since 2017 earlier this month.
“We remain concerned about the North Koreans — their attempt to continue to improve their nuclear capability as well as their ballistic missile capability,” Pentagon press secretary John Kirby told reporters Tuesday. Kirby declined to be more specific about what he was referring to on the regime’s nuclear capability.
In 2018, North Korea appeared to destroy at least three nuclear tunnels, observation buildings, a metal foundry and living quarters at its Punggye-ri nuclear test site, in a process observed by invited international journalists that CNN reported at the time.
A CNN crew at the remote mountain site in the country’s north witnessed explosions at nuclear tunnels 2, 3 and 4, from observation decks about 500 meters away. They were among two dozen journalists invited into the country to observe the apparent destruction of the site.
The move was seen at the time as North Korea making a gesture toward denuclearization to the Trump administration, but in the wake of ongoing rhetoric, then-President Donald Trump canceled a planned meeting with KimJong Un.
Officials told CNN that US and allied intelligence agencies assess that digging activities at previously shuttered underground tunnel areas is underway, which would be critical for resumption of underground nuclear testing.
North Korea has conducted six nuclear tests at the site, which lies north of Pyongyang, the most recent and powerful of which was in September 2017.
There are also indications that North Korea’s next ballistic missile test could come as soon as the next few weeks, one official said, though the official would not specify the reasons behind that assessment, and US officials say they believe Kim is likely to resume testing a nuclear weapon.
The US intelligence community estimates North Korea could be ready to conduct a nuclear test this year, according to the annual threat assessment report by the Director of National Intelligence published earlier this month. The DNI said nuclear testing and long-range missiles tests are “laying the groundwork for an increase in tensions” by the regime.
The Defense Department is considering a package of military responses to North Korea’s recent test of an improved intercontinental ballistic missiles that could range from flying bombers or sailing warships in the region to beefing up exercises and training, according to the defense officials. Japan and South Korea are being consulted on a potential decision and could be part of any show of force that is decided upon, the officials say.
The concern that nuclear testing could resume in the near future comes as North Korea has demonstrated a missile that could potentially reach the US. The Pentagon is still assessing to what extent the missile is an improved version of previous launches.
North Korea reports the missile had a maximum altitude of 3,905 miles and flew a distance of 681 miles with a flight time of 68 minutes.
The missile test was accompanied with Hollywood-style edited video complete with a soundtrack and footage of Kim in dark sunglasses with the missile behind him.
Because of the growing intelligence worries about how soon North Korea could advance it weapons program, the Pentagon earlier this month announced it was intensifying intelligence, surveillance and reconnaissance collection in the Yellow Sea and that it would increase the readiness of ballistic missile defenses in the region.
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