Mogherini says "there was awareness of the urgency" and the four ministers agreed to find some solutions within weeks.
Earlier, in response to Trump's withdrawal from the deal, France, the United Kingdom and Germany pledged their commitment to the Iran nuclear accord.
Juncker said that "I want us to agree on a common stance on our relations with the United States and its relations with Iran", hoping to stave off a negative impact of any possible USA sanctions.
The European Union is prepared to institute a so-called blocking statute to protect European companies if the Trump administration re-imposes sanctions following the U.S.'s withdrawal from the Iran nuclear deal, EU Home Affairs Commissioner Dimitris Avramopoulos said.
"We reaffirmed together our resolve to continue to implement the nuclear deal in all its parts, in good faith, and in a constructive atmosphere", she said. By that, Iran meant that unless Europe provides solid guarantees that it will maintain trade ties despite the renewed U.S. sanctions, Iran would resume uranium enrichment.
"It won't be easy, that's clear to all of us".
Iranian President Hassan Rouhani says the U.S. is wrong to think that it can dent the Palestinian nation's resistance through supporting the Israeli regime, adding that "provocative moves" by the USA and Israel will only further unite Palestinians.
At the same time, the European diplomats wanted to show they weren't gullible and wouldn't drop other divisive issues with Tehran, including its role in the Syria conflict.
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The Financial Times pointed out that while USA regulators are transacting in dollars, European envoys are mulling over setting up state credit lines in euros to get around the dollar finance restrictions with the European Investment Bank as a possible source of funding.
Rouhani said that the United States government and Israel should be answerable to the killing of people and their provocative acts in the region and added, "Unfortunately, the USA president has made miscalculations with respect to regional issues and thinks that through supporting the Zionist regime it can stifle the Palestinian nation's resistance".
Mogherini agreed at the end of a long day of diplomatic meetings. "We're not naive and know it will be hard for all sides".
As the Europeans are the closest allies of the USA, many in Iran are of this view that Washington and its close European allies have divided the task to put pressure on Tehran to succumb to their demands.
On May 11, Merkel criticized the decision of US President Donald Trump to withdraw the United States from the agreement with Iran, as she said, 'it is wrong to unilaterally cancel a pact unanimously approved by the Security Council of United Nations'.
"We have to be realistic about the electrified rail, the live wire of American extraterritoriality and how [it] can serve as a deterrent to business", Johnson told reporters in Brussels.
The US has threatened sanctions against any countries or companies continuing to do business with Iran, which has gone over poorly in European capitals. The commission is expected to unveil them to European Union leaders at a summit in Sofia, Bulgaria, on Wednesday.
European Commission head Jean-Claude Juncker presented options to protect European investment, which include retaliatory sanctions, allowing the European Investment Bank to invest in Iran, and coordinating euro-denominated credit lines from European governments.