The situation could revitalise Russian-Iranian economic ties that have been losing ground in recent years despite the involvement of Russian nuclear and oil giants in the Middle Eastern country.
A spokesman for Mrs May said: "The Prime Minister reiterated the Government's position on the Iran nuclear deal, noting that we and our European partners remain firmly committed to ensuring the deal is upheld, as the best way of preventing Iran from developing a nuclear weapon".
Re "Trump sending the world wrong message" (May 10): Regarding Linda Duryea's letter on Donald Trump withdrawing the US from Iran deal, one might consider it was Barack Obama who made the world less safe with his search for legacy. It seems clear that, from Trump's perspective, the Iran deal and the diplomatic advances with North Korea are closely related - and that his policy of "maximum pressure" is paying off. However, he added, "maybe we shouldn't be entirely surprised, but that doesn't stop me from expressing my extreme disappointment and regret with where we now are".
European firms, especially those from France and Germany, rushed to invest in Iran following the 2015 agreement, under which Tehran agreed to freeze its nuclear program in return for the repeal of punishing worldwide sanctions. It was signed in 2015.
European leaders vowed in the wake of the announcement that they would remain in the pact.
"I'm hopeful in the days and weeks ahead we can come up with a deal that really works, that really protects the world from Iranian bad behavior, not just their nuclear program, but their missiles and their malign behavior as well", he said.
Add that trump intends to immediately impose sanctions against any foreign companies that will do business with Iran.
The meeting comes amid fears that European companies may face reprisals from the USA for breaching American sanctions by continuing to operate in Iran.
The EU's executive arm, the European Commission, has been examining measures to counter the introduction of any USA sanctions that might harm European businesses and is expected to unveil them to EU leaders at a meeting in Bulgaria on Wednesday.
Pope 'very worried' by Gaza violence
Pope Francis asked all parties involved in the conflict and the whole global community to renew their promise so that dialogue, justice and peace takes precedence.
"I would like our debate to reconfirm without any doubt that as long as Iran respects the provisions of the deal, the European Union will also respect it", Tusk said in a letter to the leaders on the eve of the summit.
President Donald Trump's pullout has upset European allies, cast uncertainty over global oil supplies and raised the risk of conflict in the Middle East.
The 2015 deal offered Tehran sanctions relief in exchange for curbing its nuclear program. "It didn't bring calm, it didn't bring peace, and it never will".
The plan removed sanctions on Iran in return for Tehran giving up its military nuclear programme.
In response to Trump's assertions, O'Sullivan countered one of the key "myths" about the deal.
Following talks with British counterpart Boris Johnson, Le Drian also spoke about the 2015 nuclear agreement between Iran and the 5+1 group (China, the US, France, Britain, Russia and Germany).
Zarif said that the agreement benefits all its signatories and the illegal withdrawal from the United States should not affect the rest.
As a quid pro quo, all worldwide sanctions against Iran, the fifth largest exporter of oil, by U.S. and other countries, were lifted and Iran's economy, which had suffered all these years, was able to revive and come back to its feet.
O'Sullivan described the JCPOA as "a strategic, multilateral agreement", and "the single most important working model of nuclear nonproliferation".