"I was reassured by what I heard in my meetings on the intention to stick to the full and strict implementation of the agreement in all its part," Mogherini told France 24.
After two days of meetings with US officials, Mogherini said she will "return from Washington tomorrow reassured that the United States is committed to the full implementation of this deal."
Iran was Mogherini's priority on this visit, she said, but she also came to draw some clear lines for the new administration. The EU-US relationship may be changing, she said, but the 28-member bloc remains committed to policies on issues such as Middle East peace, refugees and Russia, even as they diverge from US positions.
"A new era in our relationship can mean that we can enter into a more pragmatic and transactional time," Mogherini said. "This can also mean that we differ in our political views from time to time and that we will be very clear on this."
Mogherini's Iran conversations with Trump officials stands in sharp contrast to the White House's public statements.
President Donald Trump has labeled the Iran nuclear agreement a "terrible deal," while National Security Adviser Michael Flynn said last week that he was "putting Iran on notice" after a January 30 missile test. New sanctions on Iran followed on February 3.
A senior Trump administration official responded to Mogherini's comments on Iran deal by saying that its intended vigilance on enforcement of the deal "would be far harder on Iran than the policy of the previous administration, which didn't seem terribly interested in enforcing the spirit of the deal. That is very much administration policy, to make sure that the agreement is being followed."
The official added, "The President is also being clear that he is reviewing all of its effects. It is not clear to me that a final policy on this been established."
On the Middle East peace process, Mogherini said the goal of a two-state solution between Israelis and Palestinians "continues to be the basis" of the body's engagement with the issue. And she critiqued the Trump administration's proposal to move the US Embassy from Tel Aviv to Jerusalem, an issue traditionally left for final-status peace talks.
"We're not moving our embassies anywhere, they stay where they are," she said. "Not only the European Union Embassy, but also those of our member states."
The Trump administration officials she spoke with, including Flynn, Secretary of State Rex Tillerson and Trump son-in-law and senior adviser Jared Kushner, agreed on the need to maintain sanctions against Russia for its aggression in Ukraine, she said, and to lift them only when the Minsk ceasefire agreement conditions are met.
On Iran, she emphasized to her US interlocutors that it's "a must that the nuclear agreement is fully implemented in all its parts by all sides," even as outside the nuclear deal, including on Iran's missile tests, terrorist activities and human rights abuses, the EU has restrictions and sanctions in place.
But she made clear that the EU would not isolate Tehran.
"The European Union and its member states continue and will continue, as the nuclear deal is implemented, to have open channels with Iran," she said. The European Union is "not introducing additional sanctions" on Iran.
And she pushed back on Trump's dismissive comments about the EU. The President said in a January interview that other EU members would follow the UK's decision to leave the union and that "I don't think it matters much for the United States."
"I'm not going to be politically correct, it's not the time or history for that," Mogherini said when asked about Trump's stance. "The European Union is here to stay."