Quoting sources including U.S. intelligence officials, it said the two facilities where North Korea has restarted construction would be graphite-moderated reactors capable of producing plutonium for nuclear warheads.

The sources said above-ground work had begun on a 50,000 kw reactor in Yongbyon, while the ground is being leveled for a 200,000 kw reactor in Taechon.

The sources said North Korea recently told the U.S. government indirectly it resumed construction of the reactors. Experts believe that with Yongbyon and Taechon under constant U.S. satellite surveillance, North Korea did so in the hope that they would discover it. The paper said the activities were on a scale easily detected by satellite.

South Korea, the U.S. and Japan believe the renewed building activity is a ploy to shake the unity between them and are likely to avoid overreacting and continue to urge North Korea to return unconditionally to six-party talks on its nuclear program, the paper said.

Washington believes the move does not immediately amplify the North Korean nuclear threat since it would take several years to finish the reactors. However, the U.S. will strengthen surveillance of the construction sites because it takes seriously the prospect that North Korea would be able to mass-produce nuclear weapons if they are completed, the Nihon Keizai said.

North Korea operates a 5,000 kw experimental graphite-moderated reactor in Yongbyon. If it ever completes the two additional reactors, the three would be capable of producing enough plutonium to make an estimated 50-55 nuclear warheads a year.

(englishnews@chosun.com )