In recent years, North Korea has doubled the size of its uranium-enriching facility, sparking fears about the country’s nuclear capabilities, The Wall Street Journal reports. Yukiya Amano, director general of the International Atomic Energy Agency, told the Journal that North Korea has ramped up activity at the facility. At the same time, North Korea is increasing its plutonium production, Amano said. Amano was a key negotiator in the 2015 agreement that capped Iran’s nuclear development but said similar negotiating tactics might not apply to North Korea. “The situation is very different. Easy comparisons should be avoided,” Amano cautioned. North Korea’s exact nuclear capabilities and stockpile are unclear. U.S. officials believe the country may have as many as 40 atomic bombs, the Journal reports.