New commercial satellite imagery is showing some of the clearest signs to date that North Korea is tunneling again at its remote underground nuclear test site in a way that could potentially shorten the time it needs for its next test. The April 3 imagery from Planet shows a new so-called crosscut tunnel, according to Jeffery Lewis, a weapons expert and professor at the Middlebury Institute of International Studies. “The telltale sign is the pile of spoil in front of the tunnel. That’s rock from inside the mountain as they dig the new tunnel,” Lewis said. The crosscut tunnel intersects with one of the main tunnels beyond the entrance, providing a shorter distance to the underground launch area. In 2018, North Korea exploded the original entrance to the tunnel but likely did not destroy the entire underground structure. This comes as North Korea may be preparing to take “another provocative action” next week in connection with Pyongyang’s April 15 holiday celebrating the birthday of the country’s founding father, Kim Il Sung, according to the State Department’s special representative for North Korea, Sung Kim. Kim told reporters Wednesday that he didn’t want to speculate about what specific action Pyongyang might take, but he raised the prospect that it could be a nuclear test, as well as another missile launch. North Korea has conducted more than a dozen missile tests this year, including several ballistic missile launches. “We are worried that in connection with the upcoming April 15 anniversary that the DPRK may be tempted to take another provocative action. We obviously hope not, but we will be prepared,” Kim said, referring to the Democratic People’s Republic of Korea, North Korea’s official name. Kim reiterated that the US has publicly and privately delivered the message to North Korea that it’s willing to engage diplomatically, but he said the US has yet to receive a response. The United States and allies believe that North Korea is beginning to prepare for a possible underground nuclear test for the first time since 2017. 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 last 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 regarding 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 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 to 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 leader Kim Jong Un. Officials told CNN that US and allied intelligence agencies assess that digging activities at previously shuttered underground tunnel areas are underway, which would be critical for the 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 last 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.