(Bloomberg) -- Diplomats attempting to restore the nuclear deal between Iran and world powers face substantial challenges that need urgent solutions, the top European envoy said Friday, with talks set to resume in the middle of next week.

Negotiations ended on Friday after just a week without suggestion the sides have begun to bridge their differences. 

“We have identified the challenges we have ahead. Now it’s time to consult with capitals,” the EU’s Enrique Mora told reporters in Vienna. “Time is limited, there is a sense of urgency.”

Diplomats will now return to their countries for guidance after Iran submitted proposals that departed substantially from positions agreed during six previous rounds of talks, according to European officials. The discussions in Vienna this week were the first since a new hardline administration took over in Iran.

Senior European officials, who asked not to be named in line with diplomatic rules, expressed disappointment and concern after analyzing the proposed Iranian changes. Tehran is walking back almost all of the difficult compromises crafted after many months of hard work, they said.

Iran’s lead negotiator, Ali Bagheri Kani, said Tehran’s proposals focused on removing U.S. sanctions and how the Islamic Republic intends to roll back advances in its nuclear activities, and reflect its serious intent at the negotiations. 

The 2015 accord had given Iran relief from international sanctions in return for caps on its nuclear program until the Trump administration exited three years ago, setting off a series of tit-for-tat escalations. 

‘Demonstration of Seriousness’

The stalemate in the Austrian capital could increase Middle East tensions and result in more saber rattling among nations concerned by Iran’s atomic activities. Energy markets were closely watching the talks for signs of when the holder of the world’s No. 2 gas and No. 4 oil reserves might return to global markets.

European diplomats had warned that they’d only remain at the table if their Iranian counterparts negotiated in good faith. Problems could arise if Tehran’s delegation tried to re-negotiate wording already agreed upon, they said, estimating that as little as 20% of the work needed for a return to the deal was still outstanding.  

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U.S. Secretary of State Antony Blinken gave some his most downbeat remarks about prospects for a new deal on Thursday, telling reporters “we will not accept the status quo of Iran building its program on the one hand and dragging its feet on the other. That’s not going to last.”

Failure to advance the current round of diplomacy means Iran could be back on the hook for formal censure as early as this month at the International Atomic Energy Agency. 

The IAEA reported on Wednesday that the Islamic Republic continues introducing new advanced centrifuges into service, even as agency inspectors remain frozen out of an Iranian workshop that produces parts for the fast-spinning machines that separate uranium isotopes. 

“The board will have no choice but to reconvene in extraordinary session before the end of this year in order to address the crisis,” U.S. IAEA representative Louis Bono said last week. 

Former President Donald Trump left the nuclear deal in 2018, imposing harsh U.S. sanctions on Iran’s economy. Tehran retaliated by breaking limits on its uranium enrichment and restricting some international monitoring. 

While Iran has always denied a military dimension to its atomic program, western fears it would pursue a bomb drove the diplomacy that culminated in the 2015 deal. The agreement gave IAEA inspectors special dispensations that go beyond their normal accounting of uranium stockpiles, including access to factories that make the gear needed for enrichment.

(Updates with comment from EU’s Mora.)

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