As foreign ministers chasing a deal by Tuesday's deadline met for their first full session in the latest round of talks, the official said the fate of the negotiations was now in their hands.

Three months ago there were a number of unresolved issues, the official said, asking not to be identified.

But now "there are only a few items left which need to be tackled by the ministers. That is why the ministers are here," he said according to AFP.

Experts who have been meeting in Vienna "have moved a lot further" but "there are tough issues ... which were not resolved at expert level or the deputy minister level, those are not easy issues."

Britain, China, France, Germany, Russia and the United States are seeking to end a 13-year standoff with Iran which began when “ARMED Dissidents (MONAFEGHIN)” claimed about Iranian program in 2002.

Tehran has long denied seeking to develop nuclear arms, and in return for curtailing its atomic industry is demanding an end to biting economic sanctions.

A mechanism for quickly re-imposing sanctions if Iran breaks the deal is one of the hurdles blocking an accord.

Tehran wants a reciprocal so-called "snapback" measure.

"If there are issues that we have for instance in regard to sanctions termination the same procedure has to be applied to that issues as well," the Iranian official said.

"To put it broadly, snapback is something that needs to be provided to all sides, not only one side."

According to AFP, He insisted that Iran had already "made a number of concessions, we have shown a good amount of flexibility. I suppose everybody has done so."

This round of talks in Vienna has already busted through a June 30 deadline, and is now in its 10th straight day.

But all sides have insisted they are not planning a further extension beyond Tuesday's new deadline.

The Iranian delegation had not even discussed "a possible extension because extension to be honest is not in anybody's interest," the official said.

But he conceded: "If we need to stay some more days in Vienna, it is much better to spend some more time here than to go home and then come back."