A U.S. expert on nuclear weapons says North Korea’s technology for enriching uranium is more sophisticated than that of Iran.

Former chief of the Los Alamos National Laboratory, Siegfried Hecker, made the statement in a report he recently submitted to the U.N. Security Council.

Hecker, who visited the North last November, said Pyongyang’s claims that it began to build a uranium enrichment facility in April 2009 do not make sense, adding that the North is likely to have been pursuing a uranium enrichment program for a very long time.

Hecker, who is currently co-director of the Stanford University Center for International Security and Cooperation, said the international community must sternly deal with the North’s nuclear weapons programs. He also stressed the need for stronger implementation of U.N. sanctions on the communist state.

Shortly after returning from a trip to the North last November, Hecker had said North Korean officials showed him a uranium enrichment facility at the Yongbyon nuclear site with two-thousand centrifuges.