The EU's foreign policy chief Federica Mogherini added that the worldwide community must also be united in preserving the deal, which she said helped make the world a safer place and prevent a nuclear arms race in the region.
Trump now will work with European partners on a follow-on agreement that enshrines certain triggers that the Iranian regime can not exceed related to ballistic missiles, said senior administration officials who briefed reporters on the decision.
Brussels-European powers will reaffirm on Thursday their support for the Iran nuclear deal that Donald Trump has rejected, EU diplomats said, on the eve of a deadline for the USA president to decide whether to reimpose oil sanctions lifted under the agreement.
He further stressed that the deal is "not renegotiable" and urged Trump to, instead of repeating exhausted rhetoric, bring the United States into full compliance of the deal, just like Iran.
Iran, which has always maintained that its nuclear program is peaceful, signed the deal with the United States, U.K., France, Russia, China, and Germany in 2015, allowing for repeated inspections of its nuclear facility in exchange for sanctions relief.
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Trump must decide by mid-January whether to continue waiving U.S. sanctions on Iran's oil exports under the terms of the pact. These are separate to the nuclear deal.
Iran's Foreign Minister Mohammad Javad Zarif said it was a "desperate attempt" to undermine a "solid" deal.
"The U.S. government, like other parties to the deal, is obliged to fulfill all its obligations, and if it fails to comply with its obligations under false pretexts, it should be fully held accountable for the consequences", the foreign ministry said in its statement.
The sanctions that Trump has to waive deal with Iran's central bank.
European powers have urged the U.S. not to abandon the 2015 agreement with Iran that limits its nuclear programme, saying it is making the world safer.
Alaeddin Boroujerdi, chairman for the Committee for Foreign Policy and National Security at the Iranian parliament, declared that Tehran will not abandon a fraction of its ballistic missile policies.
US officials and others familiar with the administration's deliberations told The Associated Press that Trump is likely to back the accord for now but that he may pair his decision with new, targeted sanctions on Iranian businesses and people.