"It is proof that diplomacy works and delivers ... The European Union will continue to work for the respect and implementation of this extremely important deal, most of all for our security," Mogherini told reporters as she went into an EU foreign ministers' meeting, AFP reported.
Trump has repeatedly blasted the nuclear accord with Iran, formally known as the Joint Comprehensive Plan of Action, as "one of the dumbest deals I have ever seen", claiming it will not stop Tehran from getting atomic weapons, an objective vigorously denied by Iran.
Totally ignorant about the numerous endorsements issued by the International Atomic Energy Agency regarding the civilian nature of Iran's nuclear program, Trump repeated the charge in interviews with top European newspapers on Sunday, according to Financial Tribune.
Mogherini said she would not comment on Trump's remarks, but said—on the first anniversary of the accord she helped negotiate— that much had been accomplished.
The agreement "has delivered both on the nuclear-related commitments Iran took and on the firm determination of the international community to fully implement this deal", she said.
As far as the EU was concerned, the accord had resulted in increased trade and economic ties, "which is really significant", she added.
British Foreign Secretary Boris Johnson, who spoke to the press ahead of the EU ministers meeting, also said the accord must be maintained.
He said it had been "a difficult and controversial deal, but one which has stopped the Iranians from acquiring nuclear technology they might otherwise have acquired, and it is a deal which we think has great merit and we want to keep going".
The accord was finally sealed in 2015, before being implemented in January 2016, with Tehran agreeing to rein in its nuclear program in return for an easing of economic sanctions.
US President Barack Obama hailed the accord as one of his major achievements, which ensured Iran's nuclear activities will remain peaceful, but Trump has said repeatedly he will ditch or rework it.
Tehran rejects any talk of renegotiating or revising the nuclear accord that has been endorsed by six world powers and a United Nations resolution.