Satellite image suggests North Korea may have resumed work on reactor

(CNN) -- North Korea has resumed work on the construction of a reactor that could help it push forward its nuclear weapons program, according to an academic group's analysis of a recent satellite image.

The blog 38 North, run by the School of Advanced International Studies at Johns Hopkins University, said Thursday that a commercial satellite image from April 30 shows the secretive regime "is now close to completion of the reactor containment building."

The building is intended to house an experimental light water reactor, according to 38 North, which is managed by Joel Wit, a former U.S. State Department official.

Work on the reactor site in Yongbyon appeared to have halted in late December, 38 North said, perhaps because of the death of the longtime North Korean leader Kim Jong Il that month, or more likely as a result of the onset of winter weather.

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Pyongyang claims the reactor is "intended to help solve domestic energy shortages," 38 North said, "but is also an important component in its effort to build nuclear weapons."

North Korea, which withdrew from the Nuclear Nonproliferation Treaty in 2003, had agreed in February to suspend nuclear activity at Yongbyon in return for shipments of food aid from the United States.

But Pyongyang then carried out a failed long range rocket launch last month that Washington said breached the terms of that deal.

The next key stage in the construction of the light water reactor would be the loading of heavy components through the roof of the reactor containment building, according to 38 North. It estimated that it would take another one to two years for the reactor facility to become operational.

South Korea has been "aware of the situation at the Yongbon complex for some time," said Cho Byung-jae, spokesman for the South's Foreign Ministry.

"Our government is currently keeping an eye on the development," he said.

North Korea carried out nuclear tests in 2006 and 2009, both of them taking place weeks or months after long range rocket launches similar to the one carried out last month.

There did not appear to be any immediate reaction to the 38 North report from Pyongyang's state-run Korean Central News Agency.

CNN's Jethro Mullen and K.J. Kwon contributed to this report.