Iran's Supreme Leader Ali Khamenei said US demands that Tehran refrain from enriching uranium are "excessive and outrageous", state media reported, voicing doubts whether nuclear talks will lead to an agreement.
"I don't think nuclear talks with the US will bring results. I don't know what will happen," Khamenei said, adding that Washington should refrain from making outrageous demands in the negotiations.
Despite expectations that a fifth round of negotiations might take place over the weekend in Rome, nuclear talks are on shaky ground as both Iran and the US have clashed on the issue of nuclear enrichment.
Deputy Foreign Minister Majid Takht-Ravanchi said on Monday that talks would fail if Washington insists that Tehran refrains from domestic enrichment of uranium, which the US says is a possible pathway to developing nuclear bombs.
Tehran says its nuclear energy program has entirely peaceful purposes.
Earlier on Tuesday, another Iranian Deputy Foreign Minister, Kazem Gharibabadi said Tehran had received and was reviewing a proposal from the United States. Last week US President Donald Trump said Tehran needed to "move quickly or something bad is going to happen."
The US president has repeatedly warned Iran it would be bombed and face severe sanctions if it did not reach a compromise to resolve its disputed nuclear program.
During his first, 2017-21 term as president, Trump withdrew the United States from a 2015 deal between Iran and world powers that placed strict limits on Tehran's enrichment activities in exchange for relief from international sanctions.
Trump, who branded the 2015 accord one-sided in Iran's favor, also reimposed sweeping US sanctions on Iran. Tehran responded by escalating enrichment.
