North Korea may soon conduct a powerful nuclear test as the reclusive country is continuing to excavate a tunnel at its nuclear site, U.S. analysts said Saturday. The news comes just a day after a former CIA official raised concerns over Pyongyang's ability to attack the U.S. with a ballistic missile.

Kim Jong Un's latest nuclear explosion may be up to 14 times more powerful than its last test, which was conducted in September 2016, South Korea's Yonhap News Agency reported, citing the analysts. Satellite images released Thursday by 38 North, a website run by the U.S.-Korea Institute at Johns Hopkins University in Washington, shows substantial tunnel excavation at the Punggye-ri nuclear test site.

"The continued tunneling under Mt. Mantap via the North Portal has the potential for allowing North Korea to support additional underground nuclear tests of significantly higher explosive yields, perhaps up to 282 kilotons (282000 tons)," according to the article written by analysts Frank Pabian, a Los Alamos National Laboratory fellow, and David Coblentz, an environmental science expert at LANL.

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North Korea's fifth nuclear test and its last so far is estimated at 15,000-20,000 tons yield. New tunneling activity has only been observed at the North Portal after the fifth nuclear test, the analysts revealed.

"This suggests that the North Portal will very likely continue to be used as the primary test location, possibly because it provides the greatest amount of overburden and would likely be the most capable of containing the largest possible explosive yields, potentially up to just above a quarter of a megaton," the report added.

North Korea continued its nuclear threats as it test-fired missiles earlier this month in retaliation to U.S.-South Korea military drills.

Bruce Klingner, a former CIA deputy division chief for Korea, told Fox News on Friday that Pyongyang is close to developing a nuclear missile that could hit Washington. While many speculate about North Korea attacking the U.S., analysts believe that the nuclear launch may come sooner than expected.

“We can expect an [intercontinental ballistic missile] test this year with full capability within the next few years,” Klingner told Fox News.

North Korea has been criticized for its latest provocation, which came just days after Pyongyang warned of “merciless military counter-actions” if Washington and Seoul provoked the reclusive country. Concerns over North Korea's nuclear attack grew after Pyongyang on Feb. 12 tested an intermediate-range ballistic missile, which it said was capable of carrying a nuclear warhead.