North Korea resumes work at its nuclear test site, analysts say

SEOUL, South Korea — North Korea has resumed work at its underground nuclear testing site, defense analysts said, as the country vowed to keep expanding its nuclear arsenal despite the latest United Nations sanctions.

The defense analysts also said the North’s Sept. 3 nuclear test, which Pyongyang said was of a hydrogen bomb, may have been much more powerful than previously estimated.

In its first official reaction to the sanctions resolution adopted by the U.N. Security Council on Tuesday, North Korea’s Foreign Ministry said Wednesday the sanctions would only strengthen the country’s resolve to pursue its nuclear weapons program “at a faster pace without the slightest diversion.”

The sanctions resolution, adopted in response to the nuclear test this month, was the ninth passed by the Security Council since North Korea’s first such test in 2006. If enforced, it would deprive North Korea of 30 percent of its annual fuel imports. It also bans imports of textiles from North Korea, stripping the country of another key source of hard currency.

But the North, already heavily sanctioned, remained defiant Wednesday, saying it would “redouble the efforts to increase its strength to safeguard the country’s sovereignty and right to existence” and establish “practical equilibrium with the U.S.”

The statement, released through the North’s state media, came at the same time a group of defense analysts, after studying recent satellite images, said they had detected new vehicles, mining carts and other signs of activity at the Punggye-ri underground nuclear test site in northeast North Korea.

“Such activity, coming shortly after the largest underground nuclear test conducted at Punggye-ri to date [via the North Portal], suggests that on-site work could now be changing focus to further prepare those other portals for future underground nuclear testing,” the defense analysts, Frank V. Pabian, Joseph S. Bermudez Jr. and Jack Liu, said in a Tuesday report on 38 North, a website focused on North Korea. The analysts gave no indication that a test appeared to be imminent.

The analysts also said the explosive yield from the Sept. 3 nuclear test may have been as much as 250 kilotons, based on revised estimates of the magnitude of the tremor created by the blast. That would be much higher than most official estimates, which have varied. Japan, for example, gave an estimate of 160 kilotons, while South Korea’s was as low as 50 kilotons.