France, Britain and Germany have said they would consider a dispute resolution mechanism enshrined in the 2015 Iran nuclear deal that could lead to United Nations sanctions being reimposed for recent breaches of the pact.
In a joint statement, the three countries, known as the E3, warned Iran that its latest actions were hindering their efforts to defuse tension in the region.
They added that they were extremely concerned by its decision to resume uranium enrichment at the Fordow plant, though stopped short of directly urging sanctions.
"Iran's action ... has potentially severe proliferation implications," the three countries said in the statement.
"We affirm our readiness to consider all mechanisms in the JCPoA (nuclear deal), including the dispute resolution mechanism, to resolve the issues related to Iran's implementation of its JCPoA commitments."
Iran is enriching uranium at its underground Fordow site and rapidly accelerating enrichment more broadly, a report by the UN atomic watchdog has found.
It is the latest in a series of steps through which it has overstepped the limits of the 2015 pact, in response to the United States withdrawing from the accord and reimposing sanctions.
"We stand ready to continue our diplomatic efforts to create the conditions for, and to facilitate, the de-escalation of tensions in the Middle East," the E3 countries said.
"These efforts are however made increasingly difficult by Iran's latest actions."
France, Britain and Germany also called on Iran to comply fully with the international atomic watchdog after one of its inspectors was detained in October.
Iran briefly held an inspector working for the International Atomic Energy Agency and seized her travel documents, diplomats told Reuters last week, in what appeared to be the first incident of its kind since the 2015 pact.