An Iranian scientist detained in the United States has left the country and is on his way back to Iran, Foreign Minister Mohammad Javad Zarif has said.
Sirous Asgari, a materials science professor from Tehran, was charged in 2016 with trying to trade secrets research from an American university.
He was acquitted by a federal court in November.
It was reported last month that Mr Asgari would be deported once he had recovered from a Covid-19 infection.
The US and Iran have denied that he is part of a prisoner swap.
In a post on Instagram on Tuesday morning, Mr Zarif welcomed what he described as the “good news” of Mr Asgari’s return on a flight to Iran, but accused the US of holding “hostage” several other Iranian scientists.
The 59-year-old professor at Sharif University of Technology was accused by US prosecutors of stealing trade secrets from a research project being carried out by Case Western Reserve University in Ohio for the US Navy.
He denied the charge and a judge eventually threw out the prosecution’s case.
His return to Iran led to speculation that he could be part of another prisoner swap.
At least six US citizens are currently imprisoned in Iran or out on bail. They include US Navy veteran Michael White, who was temporarily released from prison in March on medical grounds and is in the care of the Swiss embassy in Tehran.
In response to Mr Zarif’s Instagram post, Acting US Deputy Homeland Security Secretary Ken Cuccinelli tweeted that Mr Asgari and Mr White’s cases had “never been related”.
“We have been trying to deport Asghari since last year, being stalled every step of the way by the Iranian government. We wish Iran was so enthusiastic to get its illegal nationals back as they would have us all believe…”
He added: “… so how about the Iranians take the other 10 currently in custody with removal orders? You haven’t heard much about that, have you? If #Zarif wasn’t blowing smoke, they would’ve already made arrangements for these other 10. But instead, they stall.”
Iranian Foreign Ministry Spokesman Abbas Mousavi also said talk of a swap was “groundless”, noting that Mr Asgari was “released on the basis of being acquitted”.
In December, the US and Iran conducted a prisoner swap in a rare sign of co-operation. Chinese-American researcher Xiyue Wang and Iranian scientist Massoud Soleimani were freed.
Relations between the US and Iran have become increasingly hostile since 2018, when President Donald Trump abandoned the Iran nuclear deal.
Earlier this year, the US assassinated top Iranian commander Gen Qasem Soleimani in a drone strike in Iraq. Iran retaliated by launching ballistic missiles at Iraqi military bases hosting US forces.