Iran has released an American student who has spent the past three years in jail on spying charges in a prisoner swap.
Xiyue Wang, a Princeton University graduate student, had been sentenced to 10 years in prison after being convicted on charges of "spying under the cover of research".
The 38-year-old had been conducting dissertation research in Iran when he was detained in 2016. US officials have denied that he is a spy.
US officials told the AP news agency that Mr Wang was spending a couple of days at a military base at Landstuhl in Germany where he would undergo medical checks.
The prisoner swap, negotiated by Switzerland, saw Iranian scientist Massoud Soleimani going in the other direction.
Mr Soleimani, an expert in stem cells, was arrested at Chicago airport in 2018 and charged with attempting to violate US sanctions on Iran by exporting biological materials.
US authorities said that he had been due to be freed under the terms of a plea agreement next month.
Hua Qu, Mr Wang's wife, said: "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.
"We are thankful to everyone who helped make this happen."
"A Princeton University graduate student, Mr Wang had been held under the pretence of espionage since August 2016. We thank our Swiss partners for their assistance in negotiating Mr Wang's release with Iran.
"The highest priority of the United States is the safety and well-being of its citizens. Freeing Americans held captive is of vital importance to my Administration, and we will continue to work hard to bring home all our citizens wrongfully held captive overseas."
The prisoner swap comes despite worsening relations between Washington and Tehran since Mr Trump came to power, including the United States' unilateral withdrawal from the 2016 nuclear deal.
The Iranian foreign minister, Javad Zarif, met Mr Soleimani in Switzerland. He tweeted: "Glad that Professor Massoud Soleimani and Mr Xiyue Wang will be joining their families shortly. Many thanks to all engaged, particularly the Swiss government."
Agencies contributed to this report