Iran's supreme leader Ayatollah Ali Khamenei said US sanctions must be lifted before Tehran would return to the commitments made in the 2015 nuclear deal.
"Iran has fulfilled all its obligations under the 2015 nuclear deal, not the United States and the three European countries," Mr Khamenei told Iranian Air Force commanders and personnel.
"If they want Iran to return to its commitments, the United States must lift all sanctions first.
"This is the definitive policy of the Islamic Republic that all officials agree on."
He said Iran "will not abandon this approach".
That came hours after Iran's foreign minister urged Washington to act fast and return to the agreement.
If US sanctions are not eased by February 21, Javad Zarif said on Saturday that legislation passed by Parliament would force the Iranian government to harden its nuclear stance.
Elections in June could further jeopardise the deal, Mr Zarif said.
“Time is running out for the Americans, both because of the parliament bill and the election atmosphere that will follow the Iranian New Year," he said.
US President Joe Biden's administration is exploring ways to restore the nuclear deal that Iran signed with world powers.
The deal – known formally as the Joint Comprehensive Plan of Action – gave Iran relief from sanctions in return for curbs on its nuclear programme.
The EU and US were the main signatories in the deal, but former US president Donald Trump unilaterally withdrew from the accord in 2018 and reimposed sanctions on Tehran.
Iran retaliated by breaching the terms of the accord.
Last month, it resumed enriching uranium to 20 per cent.
Mr Biden had previously said, if Tehran returned to strict compliance with the pact, Washington would follow and use that as a springboard to a broader agreement that might restrict Iran's missile development and regional activities.
But the Biden administration is looking at ways to ease financial pressure on Iran without lifting the sanctions imposed by the Trump administration, Bloomberg reported.
It said Mr Biden’s advisers were debating several ways to ease the effect of sanctions, such as providing backing for International Monetary Fund lending to Tehran for coronavirus relief.
The US could also ease measures that stymied international aid from reaching Iran to help it fight against the spread of the virus, with advisers confident that both moves could be justified on humanitarian grounds.
Tehran continues to maintain that Washington must ease sanctions before it resumes nuclear compliance.
Iranian officials, including Mr Khamenei, ruled out negotiations on wider security issues such as the country's missile programme.
