Kerry told reporters he had spoken to Foreign Minister Mohammad Javad Zarif, who insisted Iran would live up to its promises, and the secretary said the United States would be ready to begin lifting its nuclear-related sanctions against Tehran.

"The foreign  minister made it clear to me they intend to complete obligations with respect to implementation day as rapidly as possible," Kerry said.

Earlier, Kerry had hailed the deal's "Joint Comprehensive Plan of Action, from which we are days away from implementation, if all goes well."

Kerry said Iran had shipped its stock of low-enriched uranium to Russia and that additional steps Iran was taking would leave it at least a year from achieving a nuclear capability even if it changed its mind.

Under the JCPOA plan, agreed in July between Iran and the P5+1 group of world powers, Tehran agreed to rein in its nuclear program which Western capitals alleged was aimed at building a weapon -- in exchange for sanctions relief.

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