SEOUL, South Korea — North Korea offered a rare glimpse into a secretive facility to produce weapons-grade uranium as state media reported Friday that leader Kim Jong Un visited the area and called for stronger efforts to “exponentially” increase its number of nuclear weapons. It’s unclear whether the site is at North Korea's main Yongbyon nuclear complex, but it's the North's first disclosure of a uranium-enrichment facility since it showed one at Yongbyon to visiting American scholars in 2010.