According to the Shimbun, North Korea air transported several kilograms of
fluorine gas, a requisite material for producing the "fluorinated uranium
(UF6)," a material needed for making enriched uranium, to Iran on May 20.
Now, I don't know if this source is credible, but if it is, this topic should be cause for much concern. Also, an anti-war blog discusses Why North Korea Needs Nukes.