North Korea has undertaken new work to make two new tunnel entrances at its nuclear test site in an apparent effort to prepare for future underground detonations, a U.S. think tank said Wednesday, citing satellite imagery.

Commercial aerial photos from Sept. 27 suggest continued excavation in the western part of the Punggye site, where the communist state detonated fission bombs in 2009 and February this year, according to the U.S.-Korea Institute at Johns Hopkins School of Advanced International Studies. Its first test in 2009 was conducted in the eastern part.

Imagery from a month ago shows frame work for the tunnel entrance and cart tracks. Though there were no signs to indicate any looming atomic test, further development should be spotted as it may take one to two years to complete the tunnels, SAIS said.

“These ongoing activities as well as upgrades to the site’s support areas indicate North Korea is preparing to conduct additional detonations in the future as part of its nuclear weapons development program,” said analyst Nick Hansen on the institute’s blog, 38 North.

Seoul officials remained cautious, saying no unusual activity has been detected.

“We keep a close watch on a daily basis (on the North’s move). That’s not the case,” an official at the Defense Ministry said, without elaborating.

The analysis marks the latest in a series of findings by the Washington-based think tank which pointed to possible progress in Pyongyang’s nuclear program. The Kim Jong-un regime is also believed to have reactivated its 5-megawatt graphite-moderated reactor capable of producing plutonium for weapons, apparently to boost its bargaining power in disarmament-for-aid negotiations with Washington.

After a months-long relay of war threats, the North has in recent months been calling for high-level dialogue with the U.S. and a restart of the six-nation denuclearization talks stalled for five years.

But Seoul and Washington demand that Pyongyang should first prove its sincerity with action before returning to the negotiating table. 

By Shin Hyon-hee

(heeshin@heraldcorp.com)