US Secretary of State Mike Pompeo called off a trip to Russian Federation and instead made an unscheduled visit to Brussels on Monday to hold talks with European Union officials on Iran amid renewed tensions in the Middle East, officials said.
Mogherini also said she was informed during the night of Pompeo's arrival to Brussels where European Union foreign ministers are gathered for a regular monthly meeting.
Trump spoke with Putin by telephone on May 3, and said they discussed the possibility of a new accord limiting nuclear arms that could eventually include China in what would be a major deal between the globe's top three atomic powers.
Britain's foreign minister, Jeremy Hunt, said the United Kingdom was anxious about the risk of accidental conflict between Iran and the US.
President Hassan Rouhani issued an ultimatum to the Europeans, threatening that Iran would go further if they fail to deliver sanctions relief to counterbalance US President Donald Trump's renewed assault on the Iranian economy within 60 days.
The last-minute decision - announced as Pompeo hopped on a plane - set up a confrontation between him and European diplomats who have been scrambling to save the Iranian nuclear deal which was abandoned by the USA previous year, the Washington Post reported.
A source at the USA authority told that to Reuters news agency. Because if Iran becomes a nuclear power, its neighbours are likely to want to become nuclear powers.
"This is already the most unstable region in the world and this would be a massive step in the wrong direction", he added.
Iran says the strategy amounts to "psychological warfare" and a senior Iranian Revolutionary Guards commander on Sunday said Iran would retaliate against any aggressive US moves.
Before his meeting with Pompeo, France's Foreign Minister Jean-Yves Le Drian urged Europeans to remain united in support of the nuclear deal, which was signed by the United States, Britain, France, Germany, China and Russian Federation, and which the EU helped to negotiate.
German Foreign Minister Heiko Maas said Berlin "still regards this nuclear agreement as the basis for Iran not having any nuclear weapons in the future and we regard this as existential for our security".
Iran responded by declaring it will scale back compliance with parts of the nuclear deal.
Pompeo also discussed reported attacks on several oil tankers off the coast of the United Arab Emirates on Sunday.
The United States withdrew unilaterally from it a year ago and resumed unilateral sanctions against Iran, while the referred European countries promised to create a mechanism to avoid the USA restrictions, which still does not work.