US Secretary of State Mike Pompeo threatened Iran on Sunday with more "isolation and sanctions" as the European Union strongly urged Tehran to stop actions that would undermine a landmark 2015 nuclear deal, saying it was in touch with other parties to the deal and may set up a joint commission to look into the issue.
"Iran's latest expansion of its nuclear program will lead to further isolation and sanctions. Nations should restore the longstanding standard of no enrichment for Iran's nuclear program. Iran's regime, armed with nuclear weapons, would pose an even greater danger to the world," Pompeo tweeted.
"We are extremely concerned at Iran's announcement that it has started uranium enrichment above the limit of 3.67 percent," spokeswoman Maja Kocijancic for EU foreign policy chief Federica Mogherini said earlier in a statement.
"We strongly urge Iran to stop and reverse all activities inconsistent with its commitments ... We are in contact with the other JCPoA (Joint Comprehensive Plan of Action) participants regarding the next steps under the terms of the JCPoA, including a Joint Commission," she said.
Iran announced on Sunday it will shortly boost its uranium enrichment above a cap set by the nuclear deal.
In a live news conference, senior Iranian officials threatened further violations, saying Tehran would keep reducing its commitments every 60 days, unless European signatories of protect it from US sanctions imposed by US President Trump.
"We are fully prepared to enrich uranium at any level and with any amount," said Behrouz Kamalvandi, spokesman for Iran's Atomic Energy Organization.
"In a few hours the technical process will come to an end and the enrichment beyond 3.67 percent will begin," he added, referring to the limit set in the 2015 agreement.
In a sign of heightening tensions, France, Germany and Britain -- all parties to the deal -- expressed concerns over the step taken by Tehran.
Experts fear a miscalculation in the crisis could explode into open conflict, as Trump already has nearly bombed Iran over Tehran shooting down a US military surveillance drone.