An Iranian held in the US and an American detained in the Islamic Republic have been released in an apparent prisoner swap seen as a potential breakthrough in US-Iran relations.

Iranian Foreign Minister Mohammad Javad Zarif on Saturday said Chinese-American graduate student Xiyue Wang and Iranian scientist Massoud Soleimani would be reunited with their families.   

"Glad that Professor Massoud Soleimani and Mr. Xiyue Wang will be joining their families shortly. Many thanks to all engaged, particularly the Swiss government," Zarif tweeted.

US President Donald Trump also acknowledged the release, saying: "Mr. Wang had been held under the pretense of espionage since August 2016."

"We thank our Swiss partners for their assistance in negotiating Mr. Wang's release with Iran," he added. 

Trump also thanked Iran for "very fair" negotiations in the run-up to the release.

"See, we can make a deal," said the US president.

Switzerland represents US diplomatic interests in Iran, since the two arch foes cut diplomatic ties shortly after the 1979 Islamic Revolution.

A US official told The Associated Press that the swap took place in Zurich, and that Wang is headed to Landstuhl, Germany, where he will be examined by doctors before returning to the US.

A senior US administration official later on Saturday hinted at the liberation of other Americans in Iran and saw Wang's release as a sign Tehran may be willing to enter discussions over separate political issues. The official made the comments via a conference call with reporters.

High tensions

Wang, a US citizen and Princeton University graduate student, was conducting dissertation research in Iran in 2016 when he was detained and accused of "spying under the cover of research," an allegation his family and the university have denied. He was subsequently convicted on espionage charges and sentenced to 10 years in prison in 2017.

Soleimani, a stem cell expert, was arrested at a Chicago airport in October 2018 for allegedly attempting to export biological materials to Iran in violation of US sanctions on Iran over its nuclear program.

Tensions have been running high between Tehran and Washington since Trump unilaterally withdrew the US from Tehran's nuclear deal with world powers in May 2018.

The US has since imposed harsh sanctions on Iran's economy. There have also been a series of attacks across the Middle East, which the US has blamed on Iran.

dj,jsi, sri/stb (Reuters, AP, AFP)

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