The Trump administration on Saturday announced the release of Xiyue Wang, a Chinese American graduate student detained in Iran since 2016, as part of a prisoner exchange with Tehran.

"After more than three years of being held prisoner in Iran, Xiyue Wang is returning to the United States," President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE said in a statement issued by the White House.

"We thank our Swiss partners for their assistance in negotiating Mr. Wang’s release with Iran," Trump continued. "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."

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Wang was freed from the Evin Prison in Iran and flew on a Swiss government airplane from Tehran to Zurich, where he was met by the State Department's special envoy for Iran, Brian Hook. The department tweeted a photo of the pair showing Wang holding a folded American flag.

Can’t wait to welcome you back home, @FreeXiyueWang. pic.twitter.com/C7yyeJIA5W — Department of State (@StateDept) December 7, 2019

A senior administration official said that Wang appeared to be in good health following his release and would go to Germany to undergo medical evaluations before coming to the United States.

Secretary of State Mike Pompeo Michael (Mike) Richard PompeoWatchdog confirms State Dept. canceled award for journalist who criticized Trump Trump's push for win with Sudan amps up pressure on Congress Putin nominated for Nobel Peace Prize MORE thanked the Swiss government for "facilitating" his return, saying that "Tehran has been constructive in this matter."

"We continue to call for the release of all U.S. citizens unjustly detained in Iran," he added in a statement.

The senior administration official said that negotiations have been going on for some time to secure Wang's release but more "intensely for the past three or four weeks," adding that "the Swiss took a leading role in organizing these negotiations."

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Wang, a Princeton University scholar, had been held captive in Iran since August 2016. The student was charged with espionage and in 2017 sentenced to 10 years in prison; Americans officials denied that he was a spy.

The U.S. released Iranian scientist Masoud Soleimani in exchange for Wang. Soleimani was arrested last fall on charges of violating trade sanctions against Iran and was reportedly expected to be released from prison under a plea agreement.

"This was an exceedingly good situation for the United States and Mr. Yang," the administration official said.

The official indicated that Wang could come to the White House for a visit when he feels ready, saying that "the president would like to welcome him home to America."

Iranian Foreign Minister Mohammad Javad Zarif tweeted about the prisoner exchange early Saturday, writing that the two men "will be joining their families shortly."

"Many thanks to all engaged, particularly the Swiss government," he added.

Glad that Professor Massoud Soleimani and Mr. Xiyue Wang will be joining their families shortly. Many thanks to all engaged, particularly the Swiss government. pic.twitter.com/1TeZUL0CDG — Javad Zarif (@JZarif) December 7, 2019

Wang's wife, Hua Qu, thanked those involved in securing her husband's release.

"Our family is complete once again," she said in a statement. "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."

Wang is a Chinese-born naturalized U.S. citizen whose wife and child are Chinese citizens. The Princeton graduate student traveled to Iran in 2016 to attend a Farsi language program before he was detained. His family and the university said they had not seen the indictment against him, the records from the trial or the verdict.

"The entire Princeton University community is overjoyed that Xiyue Wang can finally return home to his wife and young son, and we look forward to welcoming him back to campus," Princeton University President Christopher Eisgruber said in a statement.

"We are grateful to everyone, at Princeton and beyond, who has supported Xiyue and his family throughout his unjust imprisonment, and for all the efforts that have led to his release," he added.

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The prisoner swap comes amid broader tensions between Washington and Tehran over Iran's nuclear program and as the Trump administration has threatened to increase penalties on the country in recent days over its bloody crackdown on protesters.

Hook had briefed reporters about Iran's crackdown on Thursday, describing in graphic detail Iranian security forces firing on fleeing protesters with machine guns.

The U.S. believes that more than 1,000 people have been killed, with victims as young as 13, Hook said. As many as 7,000 demonstrators have been detained following the protests triggered by a rapid rise in fuel prices last month.

The Trump administration said this week that the U.S. would pursue sanctions against two Iranian prisons for gross human rights violations.

Trump withdrew the U.S. from the Obama-era nuclear deal with Iran but has sought to maintain a "maximum pressure campaign" on the country with economic sanctions.

The administration official on Saturday expressed optimism that the prisoner exchange might suggest openness by Iran to abandoning "the practice of hostage-taking diplomacy" in order for Tehran to receive recognition in the international community.

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"We believe the Iranians are feeling the pressure," the official said.

The official added: "We feel very good about our role in resolving the charges against Mr. Soleimani and the reciprocal humanitarian gesture by the Iranians to release Mr. Wang."

Iranian President Hassan Rouhani said earlier this week that Tehran would negotiate with the U.S. "whenever the U.S. lifts the unfair sanctions."

Updated: 10:45 a.m.