A U.S. expert on nonproliferation says North Korea is likely to have begun installing centrifuges needed for uranium enrichment as early as in June of last year.

Jeffrey Lewis, the director of the East Asia Nonproliferation Program at the Monterey Institute of International Studies, made the claim on Monday.

Lewis said that if assuming the North installed one cascade made up of 164 centrifuges once a month, the communist state is likely to have begun installing the centrifuges starting sometime between June and September of last year.

Lewis made the assessment based on a statement by former director of the Los Alamos National Laboratory, Siegfried Hecker, who visited the North earlier this month. Hecker said that he had seen what the North claimed was an enrichment facility with two-thousand centrifuges, which would translate into some 12 cascades.