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.
Several Iranian officials have said that a deal on Iran's nuclear programme is expected before the end of the week with some minor technical issues being discussed in Vienna.
According to experts, the strategy of the world powers appears to be "pressuring Iran to bring the talks to a conclusion".
Washington says it's in the "very final stages" of talks in Vienna during which US will be able to determine whether or not a mutual return to compliance with JCPOA is in the offing.
Indirect talks between Iran and US on salvaging Tehran's 2015 nuclear deal with world powers resume after a 10-day break.
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