US State Dept: Additional US sanctions to be imposed on Iran for heavy water, uranium enrichment

Washington has also revoked two waivers allowing Iran to send its excess heavy water to Oman and to export excess enriched uranium, a practice it used to remain within the strict limits of the JCPOA. In turn, Tehran received from its trade partners "yellowcake" uranium, a type of the radioactive element with a much lower concentration than enriched fuel.

"We are tightening restrictions on Iran's nuclear program as part of our pressure campaign," US Special Representative for Iran Brian Hook told Bloomberg.

Two of the three facilities given waivers have relationships with foreign countries; the heavy water reactor at Arak is being redesigned with Chinese help, according to the JCPOA; the Bushehr Nuclear Power Plant was built with help from the Soviet Union, and today Russia supplies enriched uranium for the plant and takes away its spent fuel rods. The third site, Fordow, is a uranium enrichment facility. Its inclusion in the waivers has drawn heavy criticism because of the potential for the facility to be used to produce weapons-grade plutonium, which is derived from uranium.

While US President Donald Trump and hawkish associates such as National Security Adviser John Bolton have pressed for a total cessation of all Iranian nuclear fuel refinement, the US State Department is forced to navigate a difficult and narrow path between, on the one hand, constraining Iranian production so as to avoid the perceived danger of an Iranian nuclear program, and on the other, pushing Tehran into such a desperate situation that it departs from all cooperation with the JCPOA powers and resumes its pre-2015 activities - something it's threatened to do more than once in the last year.

"Our leadership is not comfortable with any mechanism that allows uranium enrichment," Ford said. "We don't want to give Iran a supposed excuse to continue to enrich."