North Korea has offered a rare glimpse into one of its secretive uranium enrichment facilities, with leader Kim Jong Un urging the introduction of more centrifuges for the weapons-grade material needed to “exponentially increase” the number of nuclear bombs in its arsenal.

Kim inspected the country’s Nuclear Weapons Institute and the unnamed facility for producing weapons-grade nuclear materials, the official Korean Central News Agency reported Friday, without specifying the date.

Photos accompanying the report showed the North Korean leader walking with other officials in a massive hall containing row after row of centrifuges that enrich uranium by spinning it at high speeds.