Stanford University Professor Siegfried Hecker, who visited North Korea last month, says it's highly likely that a covert facility capable of highly enriched uranium (HEU) production exists in the North.

During his visit, the North disclosed to Hecker a uranium enrichment facility at its Yongbyon nuclear site.

Hecker said in a piece titled "What I Found in North Korea" in Foreign Affairs magazine that the centrifuge facility he and fellow scholars saw in the North is most likely designed to make fuel not for nuclear bombs but for light water reactors.

He said, however, that the concern is light water reactors require enriched uranium and that once enrichment capabilities are established for reactor fuel, they can be readily reconfigured to produce highly enriched uranium bomb fuel.

Hecker also said it's highly likely that a parallel covert facility capable of highly enriched uranium production exists elsewhere in the country.

He said that even more troubling than an expansion of the North's nuclear arsenal is its potential export of fissile materials or the means of producing them which now include centrifuge technologies.

He suggested that the international community redouble its efforts to shut down Pyongyang’s extensive illicit procurement network and that the U.S. reevaluate its policies on Northeast Asia.