An eighth round of talks aimed at salvaging the Iran nuclear deal kicked off in Vienna on Monday.
Tehran has maintained its focus on one side of the original 2015 bargain, demanding sanctions against it be lifted.
They've also refused to meet directly with U.S. officials, forcing the deal's remaining parties to shuttle between the two sides.
Little remains of the original deal.
It had lifted sanctions on Iran in exchange for restrictions on its nuclear activity.
Then-U.S. President Donald Trump pulled out of the deal in 2018 and reimposed sanctions.
That prompted Tehran to breach and even exceed many of those nuclear restrictions.
The previous round of talks ended a little over a week ago after adding some new Iranian demands, with Western powers warning that time was running out for negotiations.
Iran insists all U.S. sanctions must be lifted before steps are taken on the nuclear side, while Western negotiators say both demands must be balanced.
U.S. sanctions have slashed Iran's oil exports, its main source of revenue.
Tehran does not disclose data, but shipping assessments suggest a fall from around 2.8 million barrels per day in 2018 a fraction of that volume, as low as 200,000.