The Thursday meeting in Brussels is part of diplomacy on both sides of the Atlantic before deadlines related to the deal falling this month, including deciding whether to reimpose oil sanctions lifted under the deal.
The decision followed a day of discussions, including an afternoon meeting of the president's security team.
Trump also faces a deadline Friday to say whether he will "certify" to Congress that Iran is complying with the deal and that it remains in US interests to adhere to it. Trump declined to make that certification in October, throwing the deal into limbo but not breaking it outright.
"I've been warning about this for a year - that Trump is serious about walking away from the deal, and people like me who want to fix the deal and not collapse it have to get our act together and get it fixed because there are fatal flaws", said Mark Dubowitz, chief executive of the Washington-based Foundation for Defense of Democracies, who has advocated for Iran sanctions and helped Congress write them.
"The deeply flawed Obama "Iran deal" should not be a grant of immunity to Iran from sanctions related to nonnuclear activities", Sen.
"There's a great deal of criticism of the deal ever since it's been struck that the deal is a poor deal for the United States and that it wouldn't matter whether or not we were in it", he says. Nevertheless, the report concluded that the JCPOA would probably survive those trials, even though its long-term prospects remain uncertain.
The U.S. government, like other signatories to the JCPOA, is duty bound to fulfil its obligations under the JCPOA and must take consequences in case of violation.
"JCPOA is not renegotiable: rather than repeating exhausted rhetoric, United States must bring itself into full compliance - just like Iran", Zarif added, using the technical name for the 2015 nuclear deal. But the European diplomats appear to have allies in Trump's own camp.
To put it plainly, European allies have discovered that with a lot of pushing they can stop Mr Trump from pursuing what they consider disastrous foreign policies. The resulting absence of desired modifications to the deal may prove to be frustrating to the White House. Without improvements, Trump would renew his threat to withdraw from the agreement.
Iran's Foreign Minister Mohammad Javad Zarif had earlier said on Twitter that the deal was "not renegotiable" and that Trump's move "amounts to desperate attempts to undermine a solid multilateral agreement".
"There is more or less consensus that the president is going to once again decertify and continue to waive sanctions but at the same time slap new sanctions on Iran on non-nuclear issues", said Ali Vaez, an Iran specialist at the International Crisis Group.
The BBC also quoted Mogherini as saying the agreement has been "delivering on its main goal".
President must decide this week whether to waive nuclear sanctions on or effectively end the United States' participation in an worldwide accord with Tehran.
US President Donald Trump will have to decide soon on whether to continue with the Iran nuclear deal or announce its termination, three months after objecting to it and throwing the ball in Congress' court.
This is in addition to the five entities in Iran sanctioned last week and previous sanctions targeting Iran's ballistic missile program.
However, the second part involves the White House certifying that the nuclear deal remains in the USA national security interest.
The sanctions that Trump has to waive deal with Iran's central bank. "The worldwide community should be ready to deal with the consequences of such action".
Describing sanctions against Larijani as "hostile action", the foreign ministry said the move "crossed all the red lines of conduct in the worldwide community". A spokesman for Boeing replied, "Throughout this process, we have followed the USA government's lead in all our dealings with approved Iranian airlines and we will continue to do so". And according toCNBC, the Atomic Energy Organization of Iran specifically warned that it could increase uranium enrichment in response to a negative decision by the Trump administration. These areas fall outside the scope of the nuclear deal.