Mogherini says EU to stand by Iran nuclear deal

"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 said as she went into the meeting.

The political bloc's affirmation of support was also echoed by UK Foreign Secretary Boris Johnson.

Since his campaign trail, Trump has been a vocal critic of the Iran nuclear deal, promising to either scrap or renegotiate what he calls "the worst deal ever made".

The business tycoon repeated the charge in interviews on Sunday, when he also cast doubt on the future of NATO and the EU after Brexit.

Mogherini declined to comment on his remarks, however insisted that the nuclear agreement had "delivered both on the nuclear-related commitments Iran took and on the firm determination of the international community to fully implement this deal".

She added that as far as the EU is concerned, the deal had led to increased trade and economic ties.

Meanwhile, Tehran vowed on Sunday not to renegotiate the agreement that was made under Barack Obama's presidency, even if that means fresh US sanctions.

"There will be no renegotiation, and the (agreement) will not be reopened," said Araqchi, Iran's top nuclear negotiator at the talks that led to the agreement in 2015.

"We and many analysts believe that the (agreement) is consolidated. The new US administration will not be able to abandon it," Araqchi told a news conference in Tehran, held a year after the deal took effect.

"Nuclear talks with America are over, and we have nothing else to discuss," he added.

The nuclear deal, which was implemented in January 2015, is hailed as one of President Obama's major foreign policy achievements. It is seen to have prevented Iran from gaining nuclear weapons, while also avoiding war with the Islamic Republic.

This led to the lifting of punishing economic sanctions on Iran, which are likely to return once Trump is in office.