US President Joe Biden says he will not lift economic sanctions against Iran until it complies with the terms agreed under a 2015 nuclear deal.
Mr Biden was speaking in a CBS News interview aired on Sunday.
But Iran's Supreme Leader, Ayatollah Ali Khamenei, said Tehran would only return to compliance if the US first lifted all economic sanctions.
The 2015 deal sought to limit Iran's nuclear programme, with sanctions eased in return.
Former President Donald Trump, however, withdrew the US from the deal in 2018 and re-imposed sanctions, leading Iran to roll back on a number of its commitments.
Iran, which says its nuclear programme is peaceful, has been increasing its stockpile of enriched uranium. Enriched uranium can be used to make reactor fuel, but also nuclear bombs.