Iranian Massoud Soleimani and Chinese-American Xiyue Wang were released in "prisoner swap" between two countries that have seen heightened tensions recently.
ADVERTISEMENTA Chinese-American man who has been detained in Iran on spying charges has been freed in a prisoner swap.
Wang was detained in Iran in 2016 while conducting dissertation research as a Princeton University graduate student. He has been in prison on spying charges for three years.
"We thank our Swiss partners for their assistance in negotiating Mr Wang's release with Iran," US President Donald Trump said in a statement.
Iranian stem cell expert Massoud Soleimani was also freed in the swap.
Iranian foreign minister Javad Zarif tweeted photos of Soleimani and thanked the Swiss government for their assistance in the swap.
"Our family is complete once again. Our son Shaofan and I have waited three long years for this day and it's hard to express in words how excited we are to be reunited with Xiyue," Hua Qu, Wang's wife, said in a statement to Reuters.
"We are thankful to everyone who helped make this happen."
It comes at a time of heightened tension between the United States and Iran.