Iranian President Ebrahim Raisi warned Western governments Thursday he would accept no "excessive demands" in nuclear talks set to resume later this month after a five-month gap.
Diplomats on Wednesday finally announced the November 29 start date for renewed negotiations after a protracted delay since the June election of Raisi, an ultraconservative.
"We will not walk away from the negotiating table, but we will also oppose any excessive demands that would end up harming the interests of the Iranian people," Raisi said.
"We will not retreat in any way when it comes to interests of the Iranian people, but will continue our efforts to neutralise the oppressive sanctions and are taking action to have them lifted."
Raisi was speaking at a ceremony in Semnan province, east of the capital, marking the anniversary of the 1979 seizure of the US embassy in Tehran by pro-Islamic revolution students, an episode that still clouds relations.
The nuclear talks, which are being brokered by European mediators as Tehran refuses to deal with US negotiators directly, are aimed at bringing Washington back into a 2015 agreement with Iran that was abandoned by former US president Donald Trump.
President Joe Biden has said he is ready to rejoin the deal, under which Iran agreed to strict limits on its nuclear activities in exchange for relief from sweeping sanctions.
But the two sides remain at odds over the details.
Iran wants a lifting of all US sanctions which were imposed after Trump's withdrawal.
Biden's administration however says that it will only negotiate measures taken by Trump over the nuclear programme, such as a unilateral ban on oil sales -- not steps imposed on other concerns such as human rights.
Tehran also wants commitments that the United States will remain bound by the deal -- an unlikely proposition in Washington, where Trump's Republican Party fiercely opposes Biden's diplomacy with Iran.
Washington insists that Tehran must return to full compliance with the limits on its nuclear programme it agreed in 2015, and has warned repeatedly that the window of opportunity for a deal is fast closing.
Tehran and Washington have been enemies since 1979, when the government of the US-backed shah was toppled and the Islamic republic established.
Shah Mohammad Reza Pahlavi had already fled Iran after months of protests against his rule.
Seven months after the proclamation of the Islamic republic of Iran, students demanding the shah's extradition seized 52 hostages at the US embassy in Tehran and held them for 444 days, prompting Washington to sever ties.
On Thursday in Tehran, thousands of Iranians rallied outside the former US embassy chanting "Death to America" and "Death to Israel".
Many also cast doubt over the resumption of the nuclear talks later this month.
"The United States never respected treaties or kept their promises, and nothing will change," one of the protesters, Hosein Hasani, a rug merchant, said.
Maedeh Razaghnejad, a student, added: "Let's not take part in the negotiations. They have cheated us several times... we cannot trust them".
