Iran said on Friday that world powers have a “last chance” to save the 2015 nuclear deal as they meet in Vienna. "We will repeat to the Iranians that nuclear issues are not negotiable. We want them to stay in the accord, but we wont accept them messing us around," a senior European diplomat said. Irans Foreign Ministry spokesman Abbas Mousavi on Friday described the talks as a "last chance for the remaining parties ... to gather and see how they can meet their commitments towards Iran." World powers will warn Iran to stick to the terms of their nuclear deal when they meet on Friday, but with Tehran feeling the pressure from punishing US sanctions expectations of saving the accord are low, diplomats say. President Donald Trump last year pulled the United States out of the multinational deal under which sanctions on Iran were lifted in return for curbs on its nuclear program, verified by the International Atomic Energy Agency (IAEA). Washington has since re-imposed tough sanctions on Iran, aiming to cut Tehran’s oil sales to zero to force it to negotiate a broader deal that would also cover its ballistic missile capabilities and regional influence. Senior diplomats from Britain, China, France, Germany and Russia will meet with Iranian officials in Vienna on Friday, with Tehran threatening to exceed the maximum amount of enriched uranium it is allowed under the deal, adding to fears of a military escalation in the region. An Iranian official told reporters ahead of the meeting that his countrys main demand was to sell its oil at the same levels that it did before Washington withdrew from the accord. However, he cautioned that Tehran had lost patience with the European signatories. Until its demand is met, Iran will continue on its current path and go over limits of the deal one by one, starting with the uranium enrichment level, the official said, although none of the actions are irreversible. "For one year we exercised patience. Now it is the Europeans turn to exercise patience," he said. "They should try to find solutions, practical solutions and theres always enough time for diplomacy and there’s always the possibility to go back, to reverse." Going over such central limits of the deal could prompt European powers to re-impose sanctions through a process known as “snapback”. European officials have warned that Europe could go down that road, but are likely to hold back for now and wait for an assessment from the IAEA. "Europe will react cautiously. Despite strident warnings about the consequences of an Iranian violation, Europe will be reluctant to pull the plug on one of its most important multilateral accomplishments in recent years. It will instead play for time," said Eurasia analyst Henry Rome, according to Reuters. The cornerstone of European efforts to placate the Iranians is the creation of a mechanism for barter trade called Instex that would net out amounts at either end. Almost six months after it was created, it is still not operational and diplomats say it will only be able to handle small volumes for items like medicine, not the large oil sales Iran is seeking. European officials argue that it is crucial to show Iran that it is not isolated. At Fridays meeting they will demonstrate that it is progressing by offering credit lines to facilitate its implementation. But when and if there is a first transaction remains unclear. "They are impatient on Instex, but it’s complicated," said one European diplomat. "Were able to show progress now, but they say its not enough. Well thats tough luck for them. We are doing our best." The European powers will also stress their frustration with Tehran publicly pointing the finger at them.