"Nobody should seek to exploit JCPOA negotiations to obtain assurances that are separate to the JCPOA," said a statement on Saturday from the spokespersons for the British, French and German foreign ministries – the three European parties to the Vienna talks, AFP reported.
"This risks the collapse of the deal, depriving the Iranian people of sanctions lifting," the trio, known as the E3, added.
The current round of negotiations, now in its final stages, started in late November in the Austrian capital between Iran, Britain, China, France, Germany and Russia, with the US taking part indirectly.
Their aim was to revive the JCPOA which began unravelling when former US president Donald Trump withdrew from the deal in 2018 and reimposed and reinforced tough sanctions on Iran.
Last week, Russian Foreign Minister Sergei Lavrov demanded written assurances from the US that sanctions imposed on Russia over the conflict in Ukraine would not affect Moscow’s economic and military cooperation with Tehran.
The West described Russia’s new demands as “irrelevant”.
Iran said on Friday the pause in the Vienna talks may create “momentum for resolving any remaining issue and a final return” to revive the JCPOA.
"No external factor will affect our joint will to go forward for a collective agreement," Foreign Ministry spokesperson Saeed Khatibzadeh said on Twitter.
"A pause in [the] Vienna talks is needed, due to external factors," Josep Borrell, the European Union's foreign policy chief, said on Twitter.
Mikhail Ulyanov, Russia's ambassador to the UN in Vienna, told reporters outside the talks’ venue that he rejected "attempts to put all the blame on the Russian Federation", insisting that other parties to the talks "need additional time".
“Some people are trying to blame us for protracting the talks. I must tell you that the talks have not yet been finalized, even the text of a final agreement is not yet finalized,” Ulyanov said.
“Like any other participant we have the right to ask for something... It’s normal business,” he added.
"A fair and comprehensive deal is on the table ready for conclusion," the European statement said on Saturday, adding that it should be concluded with the utmost urgency.
"It is our understanding that Iran and the US have worked hard to resolve final bilateral issues and so we are ready to conclude this deal now."
Iranian Foreign Minister Hossein Amir-Abdollahian said on Friday urged the US to be realistic in joint efforts to bring the JCPOA back to life.
“Efforts to reach a good and durable agreement continue; it is within reach if US acts realistically and consistently,” he said.
On Thursday, Iran's top security official Ali Shamkhani tweeted, “The Vienna negotiations are becoming more complicated every hour without a political decision by the United States.”
The United States reaffirmed that a deal remained close and could be reached “in the coming days”.
“We’ve urged all parties… to focus on resolving the final remaining issues,” State Department spokesman Ned Price said at a news conference on Thursday.