Iran wants a guarantee that sanctions will be lifted as part of negotiations on the revival of the 2015 nuclear deal, a senior official has said.
Tehran said on Monday that failing to secure a guarantee could lead to "unfortunate events related to the agreement", with the EU suggesting the accord was under threat.
For more than a year, the EU and other world powers have been in talks with Iran aimed at restoring the Joint Comprehensive Plan of Action, which eased sanctions on Iran in return for it curbs on its nuclear programme.
The US, which has been involved in indirect talks with Iran, withdrew from the deal while Donald Trump was president.
"The most important issue for us is the guarantees. If the guarantee framework is not strong, we may see unfortunate events related to the agreement at any time," the Iranian news agency Fars quoted Foreign Ministry spokesman Nasser Kanaani as saying.
"The issue of guarantee has two sides. One is the guarantee of lifting sanctions in a way that Iran can economically benefit from the JCPOA."
Mr Kanaani said the government was also pushing for the UN nuclear watchdog to end its investigation into Iran's nuclear activities.
Tehran has been accused of failing to disclose all of its activities after nuclear material was discovered at previously undeclared research sites.
"We witnessed this incident in the previous stage. Iran unilaterally implemented the agreement, the American administration left and did not act, and the European parties did not fulfil their obligations and could not compensate the losses of the US withdrawal," Mr Kanaani said.
A deal could still be reached if "opposite parties have the political will and can act constructively", he said.
But the EU's senior diplomat Josep Borrell said on Monday that he was increasingly pessimistic about salvaging the deal.
“I am sorry to say that I am less confident today than 28 hours before about the convergence of the negotiation process, about the prospect of closing the deal right now,” Mr Borrell said in Brussels.
“If the process doesn’t converge, the whole process is in danger.”
The EU has drafted a proposal to rescue the agreement and energy traders have been closely following the talks to see whether there will be a breakthrough.
When the US withdrew from the deal it reimposed sanctions on Iran, which breached the terms of the agreement.
That has increased concerns in the West that Tehran could develop a nuclear weapon. Iran denies it has ambitions to do so.