A U.S. research center says North Korea appears to have doubled the size of a key uranium enrichment facility in a possible effort to further expand its nuclear arms program.
The Institute for Science and International Security said Wednesday new construction at the Yongbyon nuclear complex could allow for twice as many uranium-enriching centrifuges to be installed there.
North Korea revealed its uranium enrichment program three years ago. It said the plant contains 2,000 centrifuges that are only being used to produce low enriched uranium for energy generation - a claim questioned by some analysts.
The ISIS report said weapons-grade uranium could have been made at the Yongbyon plant. Or it said the uranium produced at the facility could have been further enriched at a secret centrifuge site.
Some Western nations suspect the uranium program will give North Korea an easier way to build more nuclear bombs. The North is also believed to have enough plutonium to make six to 12 nuclear weapons.
The ISIS report was based on recent satellite photos that it says showed construction at the Yongbyon centrifuge building beginning in March 2013.
Around that time, North Korea announced it would "readjust and restart all nuclear facilities in Yongbyon," including a uranium enrichment plant and a five megawatt graphite reactor. ISIS says the announcement may have been an "oblique effort" to reveal the new construction.
Experts believe that North Korea would be able to produce one to two bombs a year, if the 2,000 centrifuges at the Yongbyon plant were configured to do so. It would presumably have the capacity to produce twice that amount, if it possessed 4,000 centrifuges.
North Korea has conducted three nuclear tests in recent years. The first two, in 2006 and 2009, used plutonium. Analysts say the latest, in February, could have used highly enriched uranium.
Pyongyang is under several rounds of United Nations sanctions because of its nuclear and weapons programs. The isolated country sees the program as a deterrent against what it says are U.S. and South Korean plans for invasion.
The North and South are still technically in a state of war, since the 1950-1953 conflict ended in a truce instead of a peace treaty.