SEOUL — North Korea has increased activity at its main underground nuclear test site, digging new tunnel entrances in what could be preparations for another nuclear test, a Washington-based research institute reported Thursday.
The US-Korea Institute at Johns Hopkins School of Advanced International Studies, which based its conclusion on analysis of commercial satellite images of the site in Punggye-ri in northeastern North Korea, said there was no sign a test was imminent.
The report came a day after North Korea’s Foreign Ministry reaffirmed that the isolated country would continue to expand its nuclear arsenal, despite warnings from the United States that it will not engage in the dialogue Pyongyang is seeking until the North moves toward denuclearization.
North Korea is believed to have recently restarted a reactor at its main nuclear complex in Yongbyon, north of Pyongyang, which would revive the country’s main source of fuel for nuclear weapons, plutonium. Pyongyang is also believed to be expanding its uranium enrichment capabilities, which would provide it with an alternative fuel source for nuclear arms.
North Korea has conducted three underground nuclear tests, triggering UN sanctions, in 2006, 2009, and last February, all at the Punggye-ri site. The yield of the detonations has increased with each test, but international experts have disputed North Korea’s repeated implication that it has succeeded in making its bombs small and sophisticated enough for missile delivery. North Korea is also attempting to develop intercontinental ballistic missiles.
Speaking last month at a forum at the Asan Institute for Policy Studies in Seoul, Li Bin, a Chinese arms control expert at the Carnegie Endowment for International Peace, said he believed that North Korea had detonated a miniaturized nuclear device in its first test. But after that detonation failed to reach a normal yield, he said, the country had to increase the size of its bombs in order to boost the yield in the subsequent tests.
“The size of its reliable device today is still too big for missile delivery,” he said.
On Thursday, the US-Korea Institute said satellite photos as recent as Sept. 27 showed two new tunnel entrances at Punggye-ri, as well as growing piles of dirt. This suggested that the North might be digging new tunnels for nuclear tests or it might be building a connection to existing tunnels, the report said.
The North also appeared to be upgrading its support facilities in the area, the institute said.
These activities “indicate that North Korea is planning to conduct future detonations as part of its overall nuclear weapons development program,” the institute said in its report, posted on its website, 38 North.