Negotiations between Iran and major world powers became testy as Iran at the last minute raised the issue of eliminating broad United Nations sanctions over its conventional arms and missile programs, diplomats said.
While Iran's main focus previously has been on the economic embargoes imposed by the European Union and United States, which have crippled Iran's economy, in recent days it also started demanding that UN measures limiting its ballistic missile program and arms trade must also be scrapped as soon as the deal goes into effect.
With the clock ticking on the discussions, the debate turned emotional at a late night meeting June 6 at the Palais Coburg luxury hotel in central Vienna, where the latest round of talks has been going on since June 27.
"There was no slamming of doors, but it was a very heated exchange of views," a senior Western diplomat said.
Iranian Deputy Foreign Minister Abbas Araghchi aired his views afterwards to the press.
"An agreement only makes sense if all sanctions are lifted at the same time," he said. Western powers "must change their approach on sanctions if they want a deal... Western nations must be prepared to give up sanctions."
But the dispute is politically and emotionally charged in the West as well, because it involves Iran's backing of militant groups throughout the Middle East that are engaged in conventional battles with Israel and Western allies such as Saudi Arabia.
Among the potential beneficiaries of easier arms access for Iran, for instance, would be the Lebanese Hezbollah group and the Palestinian Hamas.
Moreover, fierce critics of Iran in the U.S. Congress would balk at any deal that gives Iran free access to conventional arms.
In view of these obstacles, a senior U.S. official insisted UN restrictions would remain on Iran's trade in arms and its access to missile technology, although he left open the possibility that these curbs might be less onerous in the future than they are at present.
Russia took Iran's side in the battle with the West over lifting the UN's broad arms embargo on Iran. Both Russia and China have been open to the idea in the past, and both would likely benefit from being able to sell arms to Iran.
Russian Foreign Minister Sergei Lavrov said the issue remains a major sticking point before leaving Vienna July 7.
"I can assure you that there remains one major problem that's related to sanctions: this is the problem of an arms embargo," he said.
With Iran having stepped up its demands, Iranian negotiators seemed in no hurry to clinch a deal, though negotiators had to extend their deadline for a third straight time, making July 10 the latest deadline.
"No deadline is sacrosanct for us," said Araghchi. "We are ready to stay in Vienna and continue talks as long as it is necessary."
But some Western negotiators portrayed the latest deadline as more definitive. U.S. officials said they still hope to wrap talks up in time to secure an expedited review by the U.S. Congress, but it was unclear if it would possible to make the July 9 deadline for submitting the plan for review.
"We've come to the end," said one top source. "We have just made one, final extension. It is hard to see how or why we would go beyond this. Either it happens in the next 48 hours, or not."