TEHERAN • Iran and the US have conducted a prisoner exchange that saw a Princeton graduate student released for an Iranian scientist, marking a potential breakthrough between Teheran and Washington after months of tensions.

Iran's Foreign Minister Mohammad Javad Zarif made the first announcement on the exchange via Twitter yesterday. The trade involves graduate student Xiyue Wang and scientist Massoud Soleimani.

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

President Donald Trump separately acknowledged Mr Wang was free in a statement from the White House, saying he "is returning to the United States".

"Mr Wang had been held under the pretence of espionage since August 2016," he said. "We thank our Swiss partners for their assistance in negotiating Mr Wang's release with Iran."

The Swiss embassy in Teheran looks out for US interests in Iran as the US embassy in the country has been closed since the 1979 student takeover and 444-day hostage crisis.

Mr Brian Hook, the US special representative for Iran, accompanied the Iranian scientist to Switzerland to make the exchange and will return with Mr Wang, according to a US official who did not want to be named.

Iran's state-run IRNA news agency later reported that Prof Soleimani was with Iranian officials in Switzerland.

Mr Wang had been sentenced to 10 years in prison in Iran for allegedly "infiltrating" the country and sending confidential material abroad. His family and Princeton University strongly denied the claims.

He was arrested while conducting research on the Qajar dynasty that once ruled Iran for his doctorate in late 19th and early 20th-century Eurasian history, according to Princeton.

Mr Wang's wife, Ms Hua Qu, released a statement saying: "Our family is complete once again."

Prof Soleimani - who works in stem cell research, haematology and regenerative medicine - was arrested by the US on charges that he had violated trade sanctions by trying to have biological material taken to Iran.

Tensions have been high between Iran and the US since President Trump unilaterally withdrew America from Teheran's nuclear deal with world powers in May last year. Since then, the US has imposed harsh sanctions on Iran's economy. There has also been a series of attacks across the Middle East that the US blames on Iran.