* Iran deal signatories meet in Vienna
* Tehran could start exceeding limits of deal soon
* Iran demands more effort to ensure oil sales
* Europeans warn on breaching nuclear terms
By Francois Murphy and John Irish
VIENNA, June 28 (Reuters) - World powers will warn Iran to stick to the terms of their nuclear deal when they meet on Friday for “last chance” talks, but with Tehran feeling the pressure from punishing U.S. sanctions expectations of saving the 2015 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 programme, verified by the International Atomic Energy Agency (IAEA).
Washington has since re-imposed tough sanctions on Iran, aiming to cut the Islamic Republic’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 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.
“We will repeat to the Iranians that nuclear issues are not negotiable. We want them to stay in the accord, but we won’t accept them messing us around,” a senior European diplomat said.
Iran’s 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.”
An Iranian official told reporters ahead of the meeting that his country’s 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 there’s 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.
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 Friday’s 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. “We’re able to show progress now, but they say it’s not enough. Well that’s 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. They say neither Russia or China, which imported some 40 percent of its oil from Iran prior to sanctions, have done much to ease Tehran’s economic woes.
“It’s about time they also stepped up,” said the diplomat. (Additional reporting by Bozorgmehr Sharafedin in London Editing by Nick Tattersall)