Iran Foreign Minister Mohammad Javad Zarif said he hoped for a "clear future design" of the deal as he began a series of diplomatic tours aimed at rescuing the agreement.
White House national security adviser John Bolton said USA sanctions on European companies that maintain business dealings with Iran were "possible", while Secretary of State Mike Pompeo said he remained hopeful Washington and its allies could strike a new nuclear deal with Tehran.
Russian FM Sergey Lavrov and his Iranian counterpart Mohammad Javad Zarif will meet on Monday in Moscow to discuss the preservation of the Iran nuclear deal following President Trump's withdrawal and renewal of U.S. sanctions.
Trump denounced the accord, completed under his predecessor Barack Obama, as a "horrible, one-sided deal that should have never, ever been made" as it did not cover Iran's ballistic missile programme or its role in Middle East conflicts. German Chancellor Angela Merkel said the remaining participants in the deal need to discuss with Tehran ways to save the agreement that may have to include sanctions-blocking measures that France's Finance Minister Bruno Le Maire said would be discussed with the European Commission.
Mogherini, who as the EU's top diplomat chaired the final stretch of 12 years of negotiations to clinch the Iran accord in July 2015 in Vienna, said: "We will all save it together".
Iran's Foreign Minister Mohammad Javad Zarif leaves after a meeting with European Union foreign policy chief Federica Mogherini at the EU Council in Brussels, Belgium, May 15, 2018.
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Those comments were echoed by Foreign Secretary Boris Johnson who told parliament that regime change in Iran was not a policy Britain should pursue.
Since the announcement, the U.S. Treasury has imposed new sanctions against Iran, making it hard for the country to make worldwide oil trades and access the global banking system.
British counterpart Johnson said the "UK and France are determined to conserve the essence of the Iran nuclear deal".
Trump's newly-named National Security Adviser John Bolton said that it is "possible" that the USA would sanction European companies that maintain business dealings with Iran, a statement that received a lukewarm reaction from Secretary of State Mike Pompeo, who said he remained hopeful that Washington and its allies European could strike a new deal with the Iranian government.
He said he spoke to U.S. Treasury Secretary Steven Mnuchin to request exceptions for French companies, a delay in implementing sanctions, and a so-called grandfather clause for companies that invested in Iran while the treaty was in place.
"We remain in the agreement and we want to keep it alive, as long as Iran respects it", he added, describing the agreement as "win-win". "We will try to uphold our side of the bargain".