Tehran has threatened to restart its uranium enrichment programme at an "industrial level" if the 2015 pact falls apart.
The comments came ahead of the first "joint commission" meeting in Vienna between the other signatories of the deal — China, Russia, France, Britain, Germany and Iran — since Washington's dramatic announcement on May 8 that it was pulling out from the Joint Comprehensive Plan of Action (JCPOA) and would re-impose sanctions on Iran.
The move has put the deal in "intensive care", the senior Iranian official said, speaking on condition of anonymity.
Iran still implementing nuclear deal: IAEA
US President Donald Trump has long trashed the deal — concluded under his predecessor Barack Obama — saying it did not do enough to curtail Tehran's nuclear ambitions.
After Friday's meeting, Iranian Deputy Foreign Minister Abbas Araghchi said negotiations were ongoing with the remaining signatories "to see if they can provide us with a package which can give Iran the benefits of sanctions lifting".
He added that "practical solutions" were required to address Iran's concerns over its oil exports, banking flows and foreign investments in the country.
"The next step is to find guarantees for that package," he said.
Araghchi said that talks would continue over the next few weeks "particularly at an expert level", after which Iran would decide whether or not to stay in the accord.
"We got the sense that Europeans, Russia and China... are serious and they recognise that JCPOA's survival depends on the interests of Iran being respected," Araghchi added.
A senior EU official said after the meeting that the bloc could not "give guarantees but we can create the necessary conditions for the Iranians to keep benefiting from the sanctions lifting under the JCPOA and to protect our interests and continue to develop legitimate business with Iran."
"We are working on a variety of measures to mitigate consequences of the US withdrawal," the official, who did not want to be named, said while cautioning that "there are things that will take more time".
Russian delegate Mikhail Ulyanov struck an upbeat note, saying: "We have all chances to succeed, provided that we have the political will.
"I must tell you that the JCPOA is a major international asset. It does not belong to the United States, it belongs to the whole international community."
Iran nuclear deal signatories meet for first time since US pullout
He added that the possibility of referring the matter back to the UN "was not discussed during this meeting".
Unusually for a meeting of the joint commission, the head of the UN's nuclear watchdog Yukiya Amano was invited to brief the participants on his organisation's work in Iran.
According to a report seen by AFP on Thursday, the International Atomic Energy Agency (IAEA) believes Iran is still abiding by the deal's key restrictions on its nuclear facilities in return for relief from damaging economic sanctions.
The IAEA, however, is "encouraging (Iran) to go above and beyond the requirements" of the deal in order to boost confidence, said a senior diplomat in Vienna, where the nuclear watchdog is based.
As well as criticising the deal for not adequately restricting Iran's nuclear activities, Trump also said it did not go far enough in limiting Iran's ballistic missile programme, or its intervention in regional conflicts from Yemen to Iraq and Syria.
The unnamed senior Iranian official rejected any attempt to link the JCPOA to other such issues.
The official said such an attempt 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.
The five signatories still committed to the agreement have said they want Iran to stay in the deal, with the European countries saying they would not rule out further talks with the Islamic Republic on an expanded text.
However, Iranian officials have warned that there was no question of broadening the discussions.
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