The European Union envoy coordinating talks on reviving the Iran nuclear deal said on Wednesday he believed a deal would be struck at the next round of talks starting next week, but other senior diplomats said "the most difficult decisions lie ahead."
"I am sure that the next round will be the one in which we will finally get a deal," Enrique Mora, chief coordinator of the talks, told reporters as the fifth round of indirect U.S.-Iranian negotiations wrapped up on Wednesday.
However, senior diplomats from Britain, France and Germany, among the major powers that struck the 2015 nuclear deal with Iran, were more cautious.
"We have continued to make progress and important parts of a future deal have now been fleshed out, but the most difficult decisions lie ahead. We have of course worked based on the principle of nothing is agreed to (until) all is agreed," the group of diplomats, known as the E3, said in a statement.
"Together we understand that time is on nobody's side. Decision time is coming up. We will reconvene next week," they added.
Two diplomats said the talks, which began in April and are in their fifth round, were expected to adjourn for a week, resuming on Thursday, June 10, though that was not set in stone.
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Such a schedule would leave only eight days to reach a pact before Iran's June 18 presidential election, which is likely to usher in a hardline president. Some delegates said that while a deal is possible by then, that timeline appears increasingly unlikely.
Mora offered his upbeat assessment after a meeting of the remaining parties to the deal - Iran, Russia, China, France, Britain, Germany - along with the EU in a format known as the Joint Commission.
Such meetings have bookended indirect talks between Iran and the United States on both countries returning to full compliance with the 2015 deal. The United States abandoned the agreement in 2018, prompting Iran to begin violating its terms a year later.
The EU chairs Joint Commission meetings in the basement of a luxury hotel and leads shuttle diplomacy between Iranian envoys and a U.S. delegation based in another luxury hotel across the road. Iran refuses to hold direct talks with Washington.
Iran's top nuclear negotiator said barriers to the revival of the deal are complicated but not insurmountable.
"Differences have reached a point where everyone believes these differences are not insolvable," Abbas Araqchi told Iranian state TV ahead of the meeting. "But the details are important and Iran's firm positions are important to be observed."
In Washington, U.S. State Department spokeswoman Jalina Porter told reporters the chief American negotiator, Rob Malley, would be returning to Washington soon and suggested the talks were making slow headway.
"Some progress has been made," she told reporters. "This isn't going to be a quick or easy process."
Iran's government spokesman on Tuesday denied that negotiations had stalled with the Islamic Republic's June 18 presidential election less than three weeks away.
The International Atomic Energy Agency's 35-nation Board of Governors holds a quarterly meeting next week, with a number of the delegates at the nuclear talks due to take part.