Uranium enrichment could give the North a second source of fissile material for weapons on top of its plutonium production program at the Soviet-era nuclear program at Yongbyon, which was frozen under a now-defunct international disarmament deal.

“The uranium enrichment facility at Yongbyon that the North disclosed to U.S. nuclear expert Siegfried Hecker is not among the three or four South Korea and the U.S. have established to be in existence,” the unnamed official was quoted as saying by the Chosun Ilbo newspaper.

“We have established that the uranium enrichment tests that the North has been conducting for some time are at separate locations,” the official said.