Iran's chief negotiator at nuclear talks in Vienna said on Saturday an understanding was emerging at the negotiations but that "serious disagreements" remained, according to Iranian state media."
"A new understanding appears to be emerging and there is a common ground between the parties on the ultimate goal," Abbas Araqchi told state media. "But the path ahead is not an easy one and there are some serious disagreements."
Earlier in the day, China's envoy to the negotiations aimed at salvaging the nuclear deal said they will continue and all remaining parties to the accord had agreed to accelerate work on issues including which sanctions the United States would lift.
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The second round of talks began on Thursday in the basement of a luxury hotel in Vienna. The United States is not present as Iran has declined face-to-face negotiation, but European Union officials chairing the talks are carrying out shuttle diplomacy with a U.S. delegation based at another hotel across the road.
Iran has breached many of the deal's restrictions on its nuclear activities in response to the U.S. withdrawal and reimposition of sanctions against Tehran under President Donald Trump. Negotiators are working on steps both sides must take, on sanctions and nuclear activities, to return to full compliance.
"All parties have agreed to further pick up their pace in subsequent days by engaging (in) more extensive, substantive work on sanctions-lifting as well as other relevant issues," China's ambassador to the UN nuclear watchdog, Wang Qun, told reporters after a meeting of the remaining parties to the 2015 deal.
Talks have been further complicated by an explosion at Iran's main uranium-enrichment facility at Natanz. Iran has responded by saying it is enriching uranium to 60 percent fissile purity, a big step towards weapons-grade from the 20 percent it had previously achieved.
Tehran says the blast it was an act of sabotage by Israel and on Saturday named a suspect. Israel has not formally commented on the incident.
Wang, the only envoy who regularly speaks to reporters outside the talks, said remaining parties to the deal - China, Russia, France, Britain, Germany and Iran - had resumed "productive and constructive work" over the past two days.
"In the next few days we hope the Joint Commission will immediately start negotiating the specific formula of sanction-lifting," he added, using the term for formal meetings of those parties.