"We really don't know if we'll get a deal or not, because the United States hasn't shown the necessary will to reach an agreement," Iranian foreign ministry spokesman Saeed Khatibzadeh said, according to the AFP news agency.
"What remains are the decisions of Washington," he added.
Iran has gradually scaled back its compliance with the 2015 deal, in response to former US President Donald Trump’s withdrawal from the agreement in May of 2018, but has held several rounds of indirect talks with the US on a return to the agreement.
Negotiations nearly reached completion last month before Moscow demanded that its trade with Iran be exempted from Western sanctions over Ukraine, throwing the process into disarray.
Earlier this month, Khatibzadeh's counterpart in the State Department, Ned Price. said it was Tehran that was not giving way to make a deal possible, but that Washington still believed there was "opportunity to overcome our remaining differences."
Khatibzadeh said on Monday that the US must cancel the "maximum pressure" campaign on Iran that Trump implemented after he withdrew from the 2015 deal.
"All components of maximum pressure must be removed. Unfortunately, the United States is trying to maintain some of the elements of maximum pressure," he said.
His comments come a day after Iran's Foreign Minister, Hossein Amir-Abdollahian, said that Washington is "imposing new conditions" in the nuclear negotiations.
"In the last two or three weeks, the American side has made excessive demands that contradict some paragraphs of the text," he said.
Among the key sticking points is Tehran's demand to delist the Revolutionary Guards from a US terror list.
Last month it was reported that the Biden administration is considering removing terrorism sanctions from the IRGC as part of negotiations to restore the 2015 Iran nuclear deal.
However, The Washington Post reported on Friday that the Biden administration plans to reject the Iranian demand.
Last week, the Pentagon's top general said he was opposed to removing the elite Quds Force of Iran's Revolutionary Guards from the US terror group list.
