A landmark nuclear deal with Tehran moved closer to implementation Monday, with U.S. Secretary of State John Kerry announcing that tons of enriched uranium that could potentially be turned to use in atomic arms were on a ship heading from Iran to Russia. Kerry hailed the development as “one of the most significant steps Iran has taken toward fulfilling its commitments” under the July 14 nuclear agreement, in comments that expanded on information The Associated Press received from a senior Russian diplomat earlier in the day. That envoy, who spoke on condition of anonymity because he wasn’t authorized to be cited by name, said Iran had permitted Russia to take possession of and ship out most of its low-enriched uranium. Low-enriched uranium is suitable primarily to generate nuclear power and needs substantial further enrichment for use in the core of a nuclear warhead. […]