Iran and the United States were preparing on Monday for a prisoner swap in the coming days, according to Lebanese media reports, a move that would represent a significant diplomatic agreement between Tehran and Washington after years of icy relations.
Lebanese broadcaster LBCI said that US national Michael White had arrived at the Swiss embassy in Tehran in preparation for the swap with Iranian scientist Sirous Asgari, who is being held in the US. Switzerland represents the United States in Iran.
Lebanese channel MTV said there would be a prisoner swap within 48 hours, without stating the identity of the prisoners.
LBCI, a private broadcaster, cited Nizar Zakka as the source of White's whereabouts. Mr Zakka is a Lebanese national and a former detainee in Iran who was released last year and flown straight to Beirut.
Iran itself said on Monday that Asgari, one of more than a dozen Iranians behind bars in the United States, is set to return to the Islamic republic within days.
Asgari was accused by a US court in 2016 of stealing trade secrets while on an academic visit to Ohio.
But the 59-year-old scientist from Tehran's Sharif University of Technology was acquitted in November.
There was no American or Iranian confirmation that White was set to be released.
The academic told British newspaper The Guardian in March that the Immigration and Customs Enforcement agency was keeping him in a detention centre in Louisiana without basic sanitation and refusing to let him return to Iran despite his exoneration.
"Dr Sirous Asgari's case has been closed in America and he will probably return to the country in the next two or three days," said Iran's foreign ministry spokesman Abbas Mousavi.
"That is, if no issues or obstacles come up," he said, quoted by semi-official news agency ISNA.
Iran's foreign ministry said last month that Asgari had contracted the novel coronavirus while in US custody.
Both Iran and the United States hold a number of each other's nationals and they have recently called for them to be released amid the Covid-19 pandemic.
Iran is battling what is the Middle East's deadliest outbreak of the virus, while the US has reported the highest total number of deaths worldwide from the disease.
Iran is holding at least five Americans and the US has 19 Iranians in detention, according to a list based on official statements and media reports.
Tensions between the two arch enemies escalated in 2018, after President Donald Trump unilaterally withdrew the US from a landmark nuclear agreement and reimposed crippling sanctions on Iran's economy.
Americans and dual nationals currently known to be held by Iran include US Navy veteran White, Siamak Namazi along with his father Baquer, Morad Tahbaz, Gholam Reza Shahini, and Karan Vafadari.
Asgari is one of the 19 held by the US, most of them dual nationals and charged with evading sanctions by either exporting goods to Iran or using the US financial system.
Long-time foes Iran and the United States have appeared to come to the brink of a direct conflict twice in the past year.
The most recent case was in January when Iran fired a barrage of missiles at US troops stationed in Iraq in retaliation for a US drone strike that killed Qasem Soleimani, a top Iranian general.