"Starting May 4, assistance to expand Iran’s Bushehr Nuclear Power Plant beyond the existing reactor unit could be sanctionable," the release said.
Iran reached a deal with Russia on the first stage of the Bushehr project — the Bushehr 1 — in 1992. Russia and Iran signed an agreement in 2014 to build the second and third reactors for the Bushehr plant.
"We will also no longer permit the storage for Iran of heavy water it has produced in excess of current limits; any such heavy water must no longer be available to Iran in any fashion," the release said on Friday.
US Department of State spokesperson Morgan Ortagus also said that the United States calls on Iran to stop all proliferation-sensitive actives and warned Tehran that transferring enriched uranium out of the country in exchange for natural uranium could be sanctionable.
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"Iran must stop all proliferation-sensitive activities, including uranium enrichment, and we will not accept actions that support the continuation of such enrichment," the release said. "Activities to transfer enriched uranium out of Iran in exchange for natural uranium could be sanctionable."