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.
Why did the nuclear deal fall apart?
Under the terms of the 2015 nuclear deal - an agreement reached between Iran, the US, China, France, Germany, Russia and the UK - Tehran agreed to limit its uranium enrichment and allow international inspectors to access sites and facilities.
In return, sanctions imposed on Tehran were lifted.
But Mr Trump withdrew the US from the deal, known as the Joint Comprehensive Plan of Action (JCPOA), in an effort to force Iran to negotiate a new accord, and reinstated economic sanctions.
Mr Trump wanted to place indefinite curbs on Tehran's nuclear programme and also halt its development of ballistic missiles.
Iran refused. In July 2019, it breached the 3.67% cap on uranium enrichment and in January this year announced it had resumed enriching uranium to 20% purity. Weapons-grade uranium is 90% purity.
In a short clip of the interview published before the full broadcast at 16:00 EST (21:00 GMT) on Sunday, Mr Biden was asked if he would halt economic sanctions to bring Tehran back to the negotiating table, and he replied: "No."
Meanwhile, Ali Khamenei said that for Iran to return to its commitments under the deal, the US must first "abolish all sanctions", Iranian state TV reported on Sunday.
"We will assess, and if we see that they have acted faithfully in this regard, we will return to our commitment," he said, adding: "It is the irreversible and final decision and all Iranian officials have consensus over it."
What else did Biden say?
The president also talked about the US relationship with China.
He said there was no reason for Washington to be drawn into direct conflict with Beijing, but that both sides would engage in what he called "extreme competition" on the global economic stage.
Mr Biden said he had not spoken to his Chinese counterpart, Xi Jinping, since becoming president last month, and that he had not changed his stance towards Beijing.
"He's very bright, he's very tough," Mr Biden said of Mr Xi, adding: "He doesn't have a democratic - small 'd' - bone in his body."
Source: BBC
