U.S. President Donald Trump hosts a roundtable discussion with small business owners and members of his administration in the Roosevelt Room at the White House December 06, 2019 in Washington, DC.

President Donald Trump on Saturday thanked Iran for releasing an American graduate student who had been imprisoned in Tehran for over three years on charges of espionage in exchange for a prisoner held in the U.S.

"Taken during the Obama Administration (despite $150 Billion gift), returned during the Trump Administration," the president wrote on Twitter. "Thank you to Iran on a very fair negotiation. See, we can make a deal together!"

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Xiyue Wang, 38, was a Princeton University doctoral student doing research in Iran when he was arrested there in August 2016 and sentenced to 10 years in prison over suspicion of being a spy.

U.S. officials have repeatedly denied that Wang, who was held in Evin Prison on two counts of espionage, was a spy.

Wang was released in Switzerland in exchange for Iranian citizen Massoud Soleimani, who was being held in an Atlanta jail over charges of violating American trade sanctions against Iran. Soleimani was expected to be released as early as January under a plea agreement.

Wang was among at least four other Americans being held in Iran.

The swap comes amid growing tensions between Iran and the U.S. and massive protests in Iran. Trump has placed significant economic sanctions on Iran and withdrew from the Obama-era Iran nuclear deal.

The protests erupted across Iran in November in response to a 50% increase in gas prices. U.S. officials believe the demonstrations have left as many as 1,000 people dead and 7,000 imprisoned, drawing widespread global criticism.

Secretary of State Mike Pompeo said Saturday that "The United States will not rest until we bring every American detained in Iran and around the world back home to their loved ones."

The White House confirmed the trade on Saturday with a statement from Trump, and Iran's foreign minister, Mohammad Javad Zarif, also confirmed the deal on twitter.