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CNN  — 

Talks to salvage the Iranian nuclear deal broke off Friday without an agreement, as negotiators left Vienna with a small number issues left unresolved amid Russian demands introduced last week that complicate a potential deal.

European Union foreign affairs chief Josep Borrell said that “a pause” in the talks in the Austrian capital “is needed, due to external factors.”

“A final text is essentially ready and on the table,” he wrote on Twitter.

“As coordinator, I will, with my team, continue to be in touch with all #JCPOA participants and the U.S. to overcome the current situation and to close the agreement,” he said.

Neither Borrell nor State Department spokesperson Ned Price said outright that the new demands by Moscow are among those “external factors.”

Last weekend, Russian Foreign Minister Sergey Lavrov said that Moscow wanted written guarantees that sanctions imposed for its invasion of Ukraine will not its impact future dealings with Tehran.

“I will be working with all delegations to overcome this situation,” Mora said.

Negotiators have met on and off in Vienna for nearly a year to try to save the agreement, which the US abandoned under the Trump administration. Iran has increasingly broken its commitments under the deal, and US and European officials have said Tehran’s nuclear advances mean that time is running out before the agreement, known as the Joint Comprehensive Plan of Action, or JCPOA, becomes defunct.

US Special Envoy for Iran Rob Malley and his team have returned to the United States as the end stage of negotiations of the Iran nuclear deal are suspended, the State Department said Friday.

“As we’ve said before, these are complex negotiations, we’re still working through a number, a very small number, but still a number, of what are undoubtedly difficult issues,” Price said at a press briefing Friday.

“There will need to be decisions made in places like Tehran and Moscow, and if that political will is there, if that seriousness of purpose is there, we remain confident that we can achieve a mutual return to compliance in fairly short order,” he said.

Price reiterated that the US sees the Iran talks and the sanctions over Russia’s invasion of Ukraine as “wholly and entirely unrelated,” and that the US has been clear with Russia “that we have no intention of offering Russia anything new or specific as it relates to these sanctions nor would that be required.”

“We regret the pause,” China’s envoy to the talks Wang Qun told reporters in Vienna on Friday.

After Lavrov’s new demand last week, Iran’s Foreign Minister responded by saying Iran will “not allow external factors” to affect the national interests of his country. On Thursday, he said that “efforts to reach a good & durable agreement continue; it is within reach if US acts realistically & consistently.”

“No single party can determine end result; a joint endeavor is needed. Reason should prevail,” Hossein Amir-Abdollahian wrote on Twitter.

Russia’s envoy, Mikhail Ulyanov separately told reporters that the “conclusion of the deal does not depend on Russia only, there are other actors who need additional time and have concerns.”

CNN’s Mostafa Salem, Adam Pourahmadi and Ellie Kaufman contributed to this report.