Iran dispatched a shipment of more than 25,000 pounds of low-enriched uranium to Russia on Monday, clearing an important hurdle in the implementation of a historic nuclear deal with the U.S. and five other world powers, Secretary of State John Kerry said.

The shipment was one of the most significant milestones yet for Iran as it works to fulfill its commitments under the July deal, Mr. Kerry said in a statement. It included Iran’s uranium enriched to 20%, except for fabricated fuel plates at a research reactor in Tehran.

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