Iran is seeking assurance from the Biden administration that a future US government will not go back on the nuclear agreement.
Analysts predict Iran could boost its oil exports by 1 million to 1.5 million barrels per day, or up to 1.5 percent of global supply, in six months, following international efforts to revive the 2015 nuclear deal.
Officials from world powers and Iran are meeting in the Austrian capital for the first time since March, when negotiations — which began in 2021 to reintegrate the United States into the agreement — stalled.
Iran refuses to hold direct talks with its arch-foe, the United States, resulting in the "proximity" talks arrangement involving European Union envoy Enrique Mora.
Qatar, a close US ally, has called for more dialogue to settle the standoff over a 2015 nuclear deal between Iran and major powers.
Tehran's decision to move the facility comes as diplomatic efforts to restore Iran’s tattered nuclear deal appear stalled.
Iran has been engaged for a year in negotiations with France, Germany, Britain, Russia and China directly, and the United States indirectly in the Austrian capital of Vienna to revive the 2015 nuclear agreement.
The European Union's Josep Borrell says the deal is at "95 percent but the last five percent is critical," as EU coordinator for the nuclear talks, Enrique Mora, travels to Tehran to close gaps in the negotiations.
Complications have surfaced after Russia demanded guarantees that Western sanctions imposed on its economy would not affect its trade with Iran, analysts say.
Extra demands made by Washington contradict its position on reaching an agreement swiftly, says Iranian FM Hossein Amirabdollahian, without specifying the demands.
The UN nuclear watchdog's Director General Rafael Mariano Grossi will meet with senior Iranian officials in Tehran to discuss the stockpile that the group says can easily be used for atomic weapons.
"Being near the finish line is no guarantee to crossing it" and sealing an accord, Iran's chief negotiator Ali Bagheri Kani says.
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