North Korea activity detected at Yongbyon nuclear complex

A North Korean guard tower overlooks the border near the North Korean city Sinuiju, across the Yalu River from Dandong, China's largest border city with North Korea. Pyongyang was engaged in some form of activity at the Yongbyon, a major nuclear facility, according to analysts. Photo by Stephen Shaver/UPI 

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SEOUL, April 4 (UPI) -- North Korea activity took place at the Yongbyon nuclear complex in February and March, weeks before Pyongyang suggested negotiationswith the United States.

Analysts William Mugford and Joseph S. Bermudez wrote on 38 North, a Johns Hopkins University website dedicated to North Korea issues, that "suspicious activity" could be seen in recent satellite imagery.

"During the past five weeks, exhaust plumes on two, possibly three, occasions were observed at the Radiochemical Laboratory's Thermal Plant," the analysts wrote, adding the activity is "unusual."

The laboratory is Yongbyon's main reprocessing installation to produce plutonium, according to Mugford and Bermudez.

The images were taken from Feb. 21 to March 21, and the analysis included before and after-activity aerial shots of North Korea's major nuclear facility.

While there is little transparency at the complex, the analysts pointed out North Korea appeared to be heating the buildings in possible preparation for "significant activity."

But whether it is for the "additional separation of plutonium for nuclear weapons remains unclear," the analysts wrote.

North Korea had called for negotiations with the United States on Sunday, issuing a lengthy statement through its National Defense Commission.

Pyongyang had called for "maintaining stability," which is "more urgent than unilateral sanctions."

South Korean newspaper Herald Business reported the North had said sanctions are hitting the country in critical ways.

"[The sanctions] extend deeply into everything, and affecting the way we live, dress and eat," North Korea had stated, according to South Korea press.