One possibility if Iran withdraws from the deal would be a return to the status quo before 2015, the official said: an intensified uranium-enrichment program that the Iranian government says is for peaceful civilian use, and economic relations with the world that are hobbled by US sanctions.
Tehran has threatened to restart its uranium enrichment program at an "industrial level" if the 2015 pact falls apart.
For the first time since the Joint Comprehensive Plan of Action (JCPOA) came into force in 2015, China, Russia, France, Britain and Germany gathered - at Iran's request - without the United States, which pulled out on May 8 and said it would re-instate sanctions.
Iran's supreme leader set out a series of conditions on Wednesday for Iran to stay in the deal.
Mr Trump denounced the accord, completed under his predecessor Barack Obama, because it did not cover Iran's ballistic missile programme, its role in Middle East conflicts or what happens after the deal begins to expire in 2025.
The 2015 agreement between Iran and world powers lifted worldwide sanctions on Tehran.
Their officials will try to flesh out with Iran's deputy foreign minister a strategy to save the deal by keeping oil and investment flowing.
He said, "Iran's missile program is completely indigenous and defensive".
The official said time was running out and that if Iran was not satisfied by European efforts, Iran would seek a ministerial meeting before making its decision.
Russian delegate Mikhail Ulyanov struck an upbeat note after the meeting, saying: "We have all chances to succeed, provided that we have the political will".
The IAEA called on Iran to remain compliant with the JCPOA and even go beyond its legal obligations in order to boost worldwide confidence in Tehran's commitments.
"The meeting will offer an opportunity to review the implications of the withdrawal of the United States from the JCPOA and discuss the way forward to ensure the continued implementation of the deal in all its aspects", the European Union said ahead of the deal.
He added that the possibility of referring the matter back to the United Nations "was not discussed during this meeting". The IAEA's director general, Yukiya Amano, briefed participants before Friday's meeting. According to a report seen by AFP Thursday, an International Atomic Energy Agency believes Iran is still abiding by the deal's key restrictions on its nuclear facilities in return for relief from damaging economic sanctions. "Israel fully supports President Trump's bold decision today to reject the disastrous nuclear deal", Israeli president Benjamin Netanyahu said, in a televised address.
The U.N. atomic watchdog policing the nuclear accord said on Thursday that Iran is still complying with the terms of the deal despite the US withdrawal, but that it could be faster and more proactive in allowing snap inspections.
The official said it would mean "we lose JCPOA and we (would) make the other issues even more complicated to resolve", adding it was pointless for the Europeans to try to "appease" Trump.
"We have now a deal which is in the intensive care unit, it's dying", the official said.
Iran's top security official says the country will maintain its advisory role in Syria and continue support for resistance groups after the USA demanded that Tehran put a halt to those activities.
The issue is expected to be discussed extensively in the talks between Swaraj and Zarif, officials said.