EU experts have already started work on measures to get round US sanctions on Iran
The European Union on Tuesday launched work on a nine-point economic plan to keep the Iran nuclear deal alive after the abrupt withdrawal of the United States.
Europe is scrambling to come up with ways to persuade Iran to stick with the landmark 2015 agreement despite US President Donald Trump ditching it a week ago.
Tehran has warned it is prepared to resume "industrial-scale" uranium enrichment "without any restrictions" unless Europe can provide solid guarantees that it can maintain the economic benefits it gained from the nuclear agreement despite Washington reimposing sanctions.
Iranian Foreign Minister Mohammad Javad Zarif met EU foreign policy chief Federica Mogherini and his counterparts from Britain, France and Germany - the three European signatories to pact - in Brussels on the last leg of a whirlwind diplomatic tour that also took in Russia and China, the two other signatory nations.
Mogherini said EU experts were aiming to come up with concrete proposals in the coming weeks on nine key issues including ensuring Iran could sell its oil and gas products and have access to international finance.
"I believe it's a good start. We're not there, we're beginning the process," Zarif told reporters after the talks.
But he warned that Tehran expected to see progress towards the guarantees it wants "within the next few weeks."
Mogherini acknowledged the enormous challenge of finding a way around US sanctions punishing businesses trading with Iran, which apply all around the world.
"We know it's a difficult task but we are detemined to do it and we have started to work to put in place measures that help ensure this happens," she told reporters.
EU experts have already started work on measures to get round US sanctions on Iran, Mogherini said.
Their efforts focus on nine key areas including maintaining economic ties with Iran, continuing Iran's ability to sell oil and gas products and protecting EU companies doing business in Iran.
The EU is also looking at how it could develop special financing vehicles for doing business with Iran.
The European Union insists the deal is working, pointing to repeated UN inspections verifying the Islamic republic's compliance with its side of the bargain.
EU leaders aim to show a united front on preserving the Iran deal when they meet for a pre-summit dinner in Sofia on Wednesday, European Council President Donald Tusk said.
"I would like our debate to reconfirm without any doubt that as long as Iran respects the provisions of the deal, the EU will also respect it," Tusk said in a letter to the leaders on the eve of the summit.
European firms, especially those from France and Germany, rushed to invest in Iran following the 2015 accord, under which Tehran agreed to freeze its nuclear program in return for an end to punishing international sanctions.