The nuclear talks with Iran have come to a stop as a result of fresh Russian demands concerning Ukraine.

 Negotiations in Vienna aimed at restoring the Iran nuclear deal were called off indefinitely Tuesday after a last-minute demand by Russia threw the talks into disarray.

In a tweet, Josep Borrell, the European Union's foreign affairs leader, announced the decision to "halt" the discussions, citing "external forces" as the reason for the break. After President Donald Trump's decision to withdraw the US from the agreement in 2018, negotiators from the seven countries involved have spent the past year hunkered in Vienna trying to find methods to resurrect the 2015 nuclear accord.

According to diplomats, Borrell was referring to Russia's demand for US sanctions relief to be applied to its future commercial dealings with Iran as a condition for participating in a revived deal, which was first made last Saturday.

A final text for a new agreement is "basically ready and on the table," according to Borrell, who added that he and his staff would keep in touch with all parties to overcome any remaining barriers and reach a conclusion.

The indefinite hiatus, on the other hand, could mark a break from which there is no way back, laying any prospect of reviving the accord to rest.

"It's a serious situation." If you lose momentum at this point, the dynamics change in such a way that it may be impossible to resume the discussions," said Esfandyar Batmanghelidj of the European Council on Foreign Relations.

According to officials, a limited number of unresolved disputes between Iran and the United States may have contributed to the impasse. They include how far the US will go to remove terrorism designations from groups like the Islamic Revolutionary Guard Corps, assurances about the easing of US sanctions, and the specifics of a prisoner exchange that might liberate US and other Western captives held in Iranian jails.

The hiatus was attributed to the difficult nature of the last stages of a negotiation, according to State Department spokesman Ned Price, who added that "external factors are also interfering" in the effort to resurrect the Joint Coordinated Plan of Action, or JCPOA, as the deal is known.

He stated that the US is not willing to make any sanctions concessions to Russia in order to revive the Iran deal, emphasizing that the new sanctions on Russia are "wholly and absolutely unrelated to the JCPOA."

Moscow's ambassador to the negotiations, Mikhail Ulyanov, told reporters that the breakdown should not be pinned completely on Russia. "There are those who need to work out their differences amongst themselves," he explained.

After the delay was announced on Friday, Iran kept its comments to a minimum. Saeed Khatibzadeh, a spokesman for the Foreign Ministry, said on Twitter that he believed the break would provide "momentum" for addressing the remaining concerns. "The main emphasis of everyone will be the successful conclusion of talks," he stated.

Meanwhile, the patience of Western allies to hold out for an agreement is wearing thin as Iran continues to advance its nuclear program. Iran has progressed its uranium enrichment and stockpiles to the point that it could be weeks away from meeting the threshold necessary to develop a nuclear bomb, and US officials have cautioned that the talks will not go on eternally.

Officials from the United States have already mentioned the prospect of enacting a "Strategy B" if the talks fail, but have not specified what that plan would entail. The alternatives range from harsher sanctions to military action, which may exacerbate the global instability caused by the Ukraine conflict by adding a second Middle East conflict to the mix.

"We haven't yet entered that hellscape. "We're basically caught in purgatory," Batmanghelidj explained.

The meetings in Vienna were aimed at sketching out a timeline for bringing the US and Iran back into compliance with the 2015 nuclear deal. Under a new agreement, the US would be expected to waive the tough new sanctions imposed after Trump's withdrawal, while Iran would be compelled to scale back its nuclear program advancements.

A settlement was so close that the Palais Coburg hotel, where the talks were held, had prepared a podium for the closing ceremony. Iran has been progressively signaling its willingness to finalize the agreement in recent weeks, diplomats said.

However, the onset of the Ukraine war has changed the geopolitical backdrop to the talks, and officials think it's now likely that the Iran deal's fate will be tied to the outcome of the conflict.

The agreement would see Iranian oil return to world markets, perhaps easing price rises caused by Russia's invasion of Ukraine and US sanctions on Russian oil. According to commentators, Russia has no interest in seeing oil prices fall, and it may believe it can use the Iran deal as leverage in future negotiations over Ukraine.

"Vladimir Putin recognizes that renewing the Iran nuclear deal is considerably more important to Joe Biden than it is to him. According to Karim Sadjadpour, a senior scholar at the Carnegie Endowment for International Peace, "Putin does not see Iran's nuclear progress as a threat, and Tehran's isolation has served Russian interests."

Iran originally reacted angrily to Russia's unexpected demand, but continued to indicate that a deal was close. However, Iranian messaging began to shift on Wednesday, with authorities pointing the finger onto the United States.

Iran's Supreme Leader Ali Khamenei gave a speech on Thursday that suggested the country was losing interest in pursuing a fresh deal. He claimed it would be a "huge mistake" to give in to US and other powers' pressure, and that it would be foolish to give up Iran's "advancement" in nuclear research. "Who will we be able to turn to in a few years if we give up now?" he wondered.

Former Vice President Mike Pence's comments to an Israeli newspaper earlier this week that a future Republican administration would withdraw from any renewed deal did not help matters, according to a senior Western diplomat who spoke on the condition of anonymity to discuss sensitive issues.

Informal negotiations are anticipated to continue, according to negotiators, with the goal of figuring out how to close the deal without Russia, which would be difficult but not impossible. Russia has been given a major role in the implementation of the agreement as the country in charge of shipping out and storing Iran's surplus enriched uranium, which would otherwise have to be shipped to another country.

According to a person familiar with the contents of the negotiations, who spoke on the condition of anonymity to discuss sensitive matters, Tehran has made it clear that it does not want to risk a public breach with Russia by turning its back on Russia's concerns and aligning with the US.

The discussions, which have involved diplomats from the UK, France, Germany, and China, as well as Iran, the US, and Russia, have been intense since the beginning of the year, and diplomats say it will be beneficial for the negotiators to take a breather. Because Iran refuses to participate in direct negotiations with the US, the Iranian and US delegations assembled in separate hotels, with officials from other countries shuttled between them.

The European Union envoy in charge of organizing the discussions, Enrique Mora, said the negotiators must take a break to "keep a positive attitude."