Federica Mogherini, the EU’s foreign policy head, said the bloc was determined to keep the 2015 agreement in place and she is due to lead talks between the foreign ministers of four countries in the pact next week.
Representatives from Iran, the UK, France and Germany are to meet in Brussels on Tuesday.
The summit will follow a string of phone calls between leaders in which they talked up efforts to preserve the deal.
Vladimir Putin and Angela Merkel spoke on Friday, a week before the German chancellor travels to Sochi, and agreed they would work to maintain the deal while seeking to avoid an escalation of regional tensions.
Mr Trump spoke to Theresa May on the phone on Friday, after which Downing Street said the prime minister “reiterated the government’s position on the Iran nuclear deal, noting that we and our European partners remain firmly committed to ensuring the deal is upheld as the best way of preventing Iran from developing a nuclear weapon”.
Meanwhile thousands of Iranians protested across the country on Friday against Mr Trump’s decision to remove the US from the nuclear agreement. France, Germany, Britain, Russia and China are the remaining signatories, alongside Iran.
Many Iranians angered by Mr Trump’s decision are now siding with hardliners who advocate suspicion of the West.
On Friday evening, the Iranian government warned it would take “whatever reciprocal measures it deems expedient” if it is not fully compensated for the US withdrawal from the nuclear agreement.
A lengthy statement called on the other countries – especially the three European powers – to safeguard the accord, implement their commitments, and “proceed from giving pledges to taking practical action without any preconditions”.
Iran reiterated that no provisions or time frames set out by the 2015 agreement “are negotiable in any manner”. It also reiterated its foreign minister was seeking “required guarantees” from the five other parties to the agreement as well as Iran’s other economic partners.
At the same time, the government said it had tasked the president of the Atomic Energy Organisation of Iran with “taking all necessary steps in preparation for Iran to pursue industrial-scale enrichment without any restrictions”.
The statement was sharply critical of Mr Trump, calling his administration “extremist” and the US withdrawal from the accord “unlawful”. It said the decision had damaged Washington’s credibility on the world stage and the credibility of other accords it has signed, and put “the present system of international law in serious danger”.
Additional reporting by agencies
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