The US has accused Iran of making “cruel” false claims that a prisoner exchange had been agreed between the two countries.
Iranian foreign minister Hossein Amir-Abdollahian on Sunday told state media a deal had been struck, which would probably be carried out soon.
But a White House security spokesperson denied this, saying Iranian officials did not hesitate to “make things up”.
The latest claim would cause heartache for affected families, they added.
Mr Amir-Abdollahian told state TV that an agreement had been reached in the recent days and “if everything goes well on the US side, I think we will witness a prisoner exchange in a short period”.
He added that Iran was ready, while the US was working on “final technical coordination”.
While insisting the claim was false, the US spokesperson said Washington was committed to securing the release of Americans held in Iran – naming Siamak Namazi, Emad Shargi and Morad Tahbaz.
Oil executive Siamak Namazi, who has dual US-Iranian citizenship, was jailed for 10 years on charges of spying and cooperating with the US government in 2016.
Emad Shargi is an Iranian-American businessman who was arrested in 2018 while working for a tech investment company.
Iranian-American environmentalist Morad Tahbaz, who also holds British citizenship, was given a 10-year sentence on charges of spying for the US and undermining Iranian security in 2019.
He released on bail last July with an electronic bracelet – with UK officials saying they were working with the US to secure his “permanent release”.
There have been tensions between the US and Iran in recent years since President Donald Trump pulled out of a nuclear deal and reimposed sanctions which severely damaged the Islamic republic’s economy.
Iran has detained a number of US-Iranian dual citizens and Iranians with US permanent residency in recent years, most of them on spying charges.
Tehran has sought the release of more than a dozen Iranians in the United States for years, including seven Iranian-American dual nationals, two Iranians with permanent US residency and four Iranian citizens with no legal status in the United States.
In 2019 the two countries conducted a prisoner swap which saw Chinese-American researcher Xiyue Wang released to the US while stem cell expert Massoud Soleimani went in the other direction.