European powers have taken action under the Iran nuclear deal to pressure Tehran into returning to compliance with the 2015 pact that has limited the country's nuclear activities.
France, Germany, and the United Kingdom are triggering a dispute resolution mechanism on Tuesday in response to Tehran's decision that it would no longer abide by a pledge to limit uranium enrichment.
EU foreign policy chief Josep Borrell, who supervises the pact, received a letter from the three countries.
Borrell said, "The aim of the dispute resolution mechanism is not to re-impose sanctions. The aim of this mechanism is to resolve issues relating to the implementation of the agreement within the framework of the joint commission."
The three nations issued a statement saying that they had no choice but to take action due to Iran's gradual escalation of its nuclear program in recent months.