European diplomats said the talks were paused at the Iranian side's request, calling the decision "disappointing," and urging Tehran to resume the negotiations quickly.
Talks aimed at salvaging Iran's tattered 2015 nuclear deal with world powers have been adjourned following a round marked by tensions over new demands from Tehran.
Participants said they aim to resume the talks by the end of 2021, though they haven't yet firmed up a date following the suspension on Friday.
"There has been some technical progress in the last 24 hours, but this only takes us back nearer to where the talks stood in June," Britain, France and Germany said in a statement after the latest talks ended.
"We are rapidly reaching the end of the road for this negotiation," they added, calling the latest pause requested by Tehran as "disappointing".
“We hope that Iran is in a position to resume the talks quickly, and to engage constructively so that talks can move at a faster pace,” the European negotiators said.
The current talks have been aimed at bringing the US back into the agreement after the Trump administration's 2018 pullout, and having Iran roll back its stepped-up nuclear activities.
“For the eighth round, we have a lot of work ahead, a very complex task, I have to say,” Enrique Mora, the talks' chairman, said. “Difficult political decisions have to be taken."
Following our consultations with other delegations, yesterday, @enriquemora_ & I met to take stock of the situation & discuss the way forward.— علی باقریکنی (@Bagheri_Kani) December 17, 2021
We have made good progress this week. We will convene a Joint Commission today & will continue talks after a break of a few days. https://t.co/IcBJiNagdF
'Losing precious time'
Following the US decision to withdraw from the deal and reimpose sanctions on Iran, Tehran had taken successive steps to increase its nuclear activities.
Washington has been indirectly participating in the talks, and President Joe Biden has signalled that he wants to rejoin the deal.
Diplomats from the three European nations have voiced frustration with Iran's stance during the current talks, warning of "losing precious time dealing with new Iranian positions inconsistent with the JCPOA or that go beyond it.”
Still, there was one sign of progress when Iran and the International Atomic Energy Agency reached a deal to reinstall cameras at an Iranian site that manufactures centrifuge parts.
Mora underscored that there is a “sense of urgency” to revive the 2015 agreement after the talks adjourned, though he wouldn't set a deadline.
“We are not talking any more about months, we are talking about weeks,” he said, though he added that he could not say how many.
Iranian officials did not explain why they had requested a break other than to say there would be consultations in Tehran.