Iran and the United States have exchanged nationals in a move that could mark a breakthrough between Tehran and Washington after months of tensions.
The swap on December 7 involved Xiyue Wang, a Princeton graduate student detained by Iran, and Masud Soleimani, an Iranian scientist held by the United States.
In a White House Statement, U.S. President Donald Trump acknowledged Wang was free, saying he "is returning to the United States."
Later in the day, Trump thanked Iran on Twitter for what he called "a very fair negotiation."
"See, we can make a deal together," he wrote.
Earlier, Iranian Foreign Minister Mohammad Javad Zarif announced on Twitter that the exchange would happen soon.
"Glad that Professor Massoud Soleimani and Mr. Xiyue Wang will be joining their families shortly," Zarif wrote. "Many thanks to all engaged, particularly the Swiss government."
The Swiss Embassy in Tehran looks out for U.S. interests in the country as the U.S. Embassy there has been closed since the 1979 student takeover and 444-day hostage crisis.
Iran's state-run IRNA news agency later reported that Soleimani was with Iranian officials in Switzerland.
Brian Hook, the U.S. special representative for Iran, accompanied the Iranian scientist Soleimani to Switzerland to make the exchange and will return with Wang, according to a U.S. official who spoke on condition of anonymity as the information had yet to be released.
Hook and Wang were en route to Landstuhl hospital at Ramstein Air Base in Germany where Wang will be examined by doctors, the official told the AP news agency.
Xiyue Wang, a U.S. citizen and Princeton University graduate student, was conducting dissertation research in Iran in 2016 when he was detained and accused by Iranian authorities of "spying under the cover of research," an allegation his family and the university deny.
He was subsequently convicted on espionage charges and sentenced to 10 years in prison in 2017.
Soleimani, a stem cell expert, was arrested at Chicago airport in October 2018 for allegedly attempting to export biological materials to Iran in violation of U.S. sanctions on Iran over its nuclear program.
Tensions have been high between Tehran and Washington since May 2018 when Trump unilaterally withdrew the United States from the international agreement to curb Iran's nuclear program and reinstated harsh sanctions that have crippled the Iranian economy.