The United States acted on Friday to force Iran to stop producing low-enriched uranium and expanding its only nuclear power plant even as it granted waivers allowing some countries to conduct civilian nuclear cooperation with the country. In line with the 2015 nuclear deal, which was negotiated under former president Barack Obama and still enjoys strong support among European powers, Iran was limited to keeping 300 kilograms of uranium enriched up to 3.67 percent -- far below the level needed to build nuclear weapons. As part of the agreement, Iran was to sell any enriched uranium above that threshold on international markets in return for natural uranium, with Russia a key player. But in Fridays policy change, Secretary of State Mike Pompeo said the United States would start to impose sanctions on anyone involved in the trade of natural for enriched uranium -- as well as in the storage of Iranian heavy water that was in excess of limits. "The Trump administration continues to hold the Iranian regime accountable for activities that threaten the regions stability and harm the Iranian people. This includes denying Iran any pathway to a nuclear weapon," State Department spokeswoman Morgan Ortagus said. At the same time, Pompeo renewed waivers of US sanctions allowing Russia, China and European countries to pursue cooperation programs designed to prevent Iran from reactivating a defunct nuclear weapons program. Facilities in the waiver extensions include the Bushehr nuclear power plant, the Fordow enrichment facility, the Arak nuclear complex and the Tehran Research Reactor, the State Department said. But, it said, the renewable waivers would be granted only for 90 days, a shorter period than the previous 180 days. The moves are part of the Trump administrations efforts to impose international political and economic isolation on Tehran that began with the US withdrawal in May 2018 from the nuclear deal. It was the third punitive action taken against Iran in as many weeks. Last week, it said it would grant no more sanctions waivers for countries buying Iranian oil, accelerating its plan to push Irans oil exports to zero. The Trump administration also took the unprecedented step of designating Irans Revolutionary Guard Corps as a foreign terrorist organization.