Sources close to the nuclear talks underway between Iran and the world powers in Vienna said Iranian Foreign Minister Mohammad Javad Zarif has warned EU Foreign Policy Chief Federica Mogherini to avoid threatening Iran.

Sources close to the nuclear talks underway between Iran and the world powers in Vienna said Iranian Foreign Minister Mohammad Javad Zarif has warned European Union Foreign Policy Chief Federica Mogherini to avoid threatening Iran, Fars news agency reported.

Russian sources said on Wednesday that the atmosphere of the talks soured somehow a few days ago during a meeting between Zarif and Mogherini, the minister of the Group 5+1 (the US, Russia, China, Britain and France plus Germany).

"And then at some stage, when the Iranian officials seriously defended their positions, Mogherini warned to leave the talks, saying the negotiations couldn't go on and every one had better return home as long as the conditions prevailing over the meeting continued," the diplomat added.

"Zarif immediately replied, telling Mogherini "never threaten an Iranian!", followed by his Russian counterpart Sergey Lavrov who said "or a Russian!".

Iran and the 6 world powers are in the final phase of their last round of talks in Vienna to draft a final deal to end their over-a-decade-long nuclear standoff.

Iran's deputy lead negotiator Abbas Araqchi said on Tuesday his country and the six world powers won't have a deal as long as the US is adamant in its decision to maintain the sanctions policy.

The deputy chief negotiator pointed out that there have only remained "7 to 10 issues of difference between Iran and the G5+1, and explained that "only 2 or 3 of them are fundamental and important".

"The rest are minor technical issues" which are not that much important, Araqchi continued.

The Geneva interim deal envisaged the removal of all the UN and unilateral US and EU sanctions against Iran under a final comprehensive deal.

Also, in a framework agreement approved by the six powers and Iran in April known as the Lausanne Statement, the seven nations agreed that a final deal would include removal of all sanctions as well as a UN Security Council resolution which would call all the five UNSC sanctions resolutions imposed against Iran's nuclear activities as "null and void".

The first two UNSC resolutions boycotted export of military, specially missile, hardware and software to Iran, a sanction that would be automatically removed under the new UNSC resolution that, according to the Lausanne framework agreement, should be issued on the same day that the final deal is endorsed.