By Staff, Agencies

A senior US State Department official said negotiators have made significant progress regarding Iran nuclear deal and it's in a better position, but added some serious issues still remains.

Negotiators made significant progress in the last week or so on an agreement to revive the 2015 Iran nuclear deal, a senior US State Department official has told reporters; claiming, however, that very tough issues remain.

"There's been significant progress over the last week or two. We have significantly narrowed the areas that still need to be resolved. And so, in that sense, there has been progress that has been moving towards a potential deal," the official said on Friday.

 "So we are in a better position than we have been. But at the same time, it's important to note that very serious issues remain."

For his part, Mohammad Eslami, head of the Atomic Energy Organization of Iran, said the Islamic Republic can resume production of highly enriched uranium "at any moment" if the US again pulls out of a nuclear deal with major powers.

Eslami made the remarks as talks in Vienna on bringing Washington back into the 2015 agreement abandoned by former US President Donald Trump reach a critical stage.