In a joint statement Tuesday, the foreign ministers of Germany, France and Britain and the European Union's foreign policy chief said that "we have been consistent and clear that our commitment to the nuclear deal depends on full compliance by Iran." They called for Iran to reverse the move "and to refrain from further measures that undermine the nuclear deal."
They added that they "are urgently considering next steps" under the terms of the agreement in close coordination with other signatories. The three European countries, Russia and China remained on board the 2015 deal meant to curb Iran's nuclear ambitions after the United States withdrew last year.
A visiting Iranian official has briefed Syrian President Bashar Assad on the country's nuclear deal with world powers and rising tensions in the region.
According to Assad's office, the Syrian leader told Iran's Assistant Foreign Minister Ali Asghar Khaji during their meeting Tuesday that Damascus stands by Tehran and its people against the threats.
Iran is one of Assad's strongest allies and has sent fighters it backs to fight along Syrian government forces against the opposition during the country's eight-year conflict.
The crisis gripping the Middle East stems from U.S. President Donald Trump's withdrawal a year ago from the nuclear deal between Iran and other world powers and then imposing crippling new sanctions on Tehran.
Russia's top diplomat has urged Iran to fulfill its obligations under its nuclear deal with world powers while calling on Europe to offer relief from U.S. sanctions.
Russian Foreign Minister Sergey Lavrov said Tuesday that the U.S. sanctions have effectively prevented Iran from selling the excess uranium it produces, contributing to its stockpiling.
He called on Tehran to "show restraint, not yield to emotions" and observe provisions of the deal.
Iran acknowledged Monday it had exceeded the limit set on its low-enriched uranium stockpiles by the 2015 nuclear deal, its first major breach of the agreement a year after the U.S.'s unilateral withdrawal.
Lavrov also urged the European Union to make good on its pledge and finally implement a working system protecting its trade with Iran from American sanctions.
China has expressed regret over Iran's move to break limits on its stockpile of low-enriched uranium, but says Washington's pressure campaign is the root cause of tensions.
Foreign ministry spokesman Geng Shuang told reporters Tuesday that Beijing remains committed to the 2015 agreement, known as the Joint Comprehensive Plan of Action. He said all parties should exercise restraint and safeguard the agreement to "avoid escalating tensions."
Geng said that Beijing expressed its "regret" over Iran's recent moves, but added: "As we have repeatedly stressed, the U.S. 'maximum pressure' is the root cause of the current tension on the Iranian nuclear issue."
China was a signatory to the joint plan along with Britain, France and Germany, and has struggled to keep Iran within it after the U.S. unilaterally pulled out last year.
France's president is urging Iran to immediately reduce its stockpiles of low-enriched uranium and stick to the terms of the 2015 nuclear deal with world powers.
Emmanuel Macron said in a statement Tuesday that he "took note with concern" of Iran's announcement that it has surpassed the limit of 300 kilograms (661 pounds) of low-enriched uranium laid out in the accord.
Macron asked Iran also abstain from any other steps that would threaten the deal, which promised to lift trade sanctions in exchange for curbing Iran's atomic program.
France strongly opposed President Donald Trump's decision to withdraw the U.S. from the deal and impose new sanctions on Iran.
Macron said France will try to make sure Iran honors its commitments, as well as receives the "economic advantages of the accord."