In 2013, North Korea doubled the size of its uranium centrifuge facility.
John Bolton, US ambassador to the United Nations from August 2005 to December 2006, wrote on April 30, 2015 "Tehran and Pyongyang have cooperated on ballistic missiles since at least 1998 ... numerous reports have emerged of Iranian and North Korean scientists exchanging visits and potentially valuable information. What if Pyongyang is already hosting an extensive Iranian-enrichment program, deeply buried somewhere in its half of the peninsula? What if some of the estimated 20 warheads are actually Iranís property, having been manufactured and now stored far from Tehran to avoid detection? East Asian experts have long looked through a stovepipe at North Korea, and Middle East experts gaze through their own stovepipe at Iran."