Washington: "The right amount of uranium enrichment for the world's largest state sponsor of terror is zero ... There is no legitimate reason for Iran to resume enrichment at this previously clandestine site," U.S. Secretary of State Mike Pompeo told reporters.
The United States said it will no longer waive sanctions related to Iran's Fordow nuclear plant after Tehran resumed uranium enrichment at the underground site.
"The right amount of uranium enrichment for the world's largest state sponsor of terror is zero ... There is no legitimate reason for Iran to resume enrichment at this previously clandestine site," U.S. Secretary of State Mike Pompeo told reporters.
The U.N. atomic watchdog and Iran itself said this month Tehran is again enriching uranium at the sensitive site, which Iran hid from U.N. non-proliferation inspectors until its exposure in 2009.
While European countries have tried to salvage the 2015 nuclear nonproliferation agreement, Iran has increasingly distanced itself from the accord since the United States withdrew last year.
The pact requires Iran to restrain its enrichment programme in exchange for the removal of most international sanctions, and it called for Fordow to be converted into a nuclear, physics and technology centre.
Despite its withdrawal, the Trump administration has granted sanctions waivers that allowed foreign firms to do work in Iran that advanced non-proliferation. Those included Russia's Rosatom at Fordow.
Pompeo said the waivers will end on Dec. 15. The State Department had said last month that it renewed waivers for 90 days.
Republican Senators Ted Cruz, Lindsey Graham and Liz Cheney praised the decision and called on the Trump administration to also end the waiver for the Arak heavy water reactor, where Chinese state-owned China National Nuclear Corp has operated.
"There is no justification for extending that waiver in light of recent confirmation that Iran is violating its heavy water obligations, let alone for letting Iran continue to build up its programme â€“ not at Fordow, and not at Arak," the senators said in a statement.
Kelsey Davenport, director of the Arms Control Association, said Monday's decision could further jeopardize the nuclear accord, known as the Joint Comprehensive Plan of Action.
"This step further risks collapsing the JCPOA because it removes a tangible benefit to Iran under the deal," Davenport said.
Pompeo also called on Iran to end violence against protesters, as demonstrations have spread across the Islamic Republic since Friday. Iran's powerful Revolutionary Guards warned on Monday of action if unrest over gasoline price hikes does not cease. At least 100 banks and dozens of buildings and cars have been torched, state media reported.
"We condemn strongly any acts of violence committed by this regime against the Iranian people and are deeply concerned by reports of several fatalities," Pompeo said.