PRINCETON, N.J. (Reuters) - By the time Princeton University graduate student Xiyue Wang arrived in Iran to conduct research for his doctorate in history, he had already spent years living and working in politically turbulent countries.

Xiyue Wang, a naturalized American citizen from China, arrested in Iran last August while researching Persian history for his doctoral thesis at Princeton University, is shown with his wife and son in this family photo released in Princeton, New Jersey, U.S. on July 18, 2017. Courtesy Wang Family photo via Princeton University/Handout via REUTERS

The Chinese-born U.S. citizen previously worked as a Pashto translator for the International Committee of the Red Cross in Afghanistan and spent time in Uzbekistan while a student at Harvard University.

Wang, 37, was sentenced to 10 years in prison on spying charges after his arrest last summer, an Iranian official said on Sunday. He is the latest American citizen to face jail in Iran for what the U.S. State Department has denounced as fabricated charges.

His sentencing shocked his colleagues at Princeton, who described him in interviews as a quiet but collegial scholar whose intellectual curiosity stood out even at the elite school in New Jersey.

Wang is married and has a 4-year-old son. In addition to Pashto, English and his native Mandarin, Wang is also proficient in Russian and Turkish and was learning Persian in Iran.

His wife, Hua Qu, said in a statement on Tuesday that her husband “has been unjustly imprisoned for espionage that I know he did not and never would commit.”

“We fervently hope that the Iranian authorities will release him soon so that he can return home to his young family,” she added.

University President Chris Eisgruber said in a letter to the school on Monday that Princeton had kept his arrest confidential on the recommendation of advisers inside and outside of government.

Wang, a history student at Princeton since 2013, was conducting field work for his dissertation, which is focused on how Muslim regions are governed.

Iran accused him of scanning 4,500 pages of digital documents. His academic adviser, history Professor Stephen Kotkin, and fellow graduate students said in interviews that scanning historical documents – the ones Wang was studying were a century old, Kotkin said – for later review is a common practice for researchers.

Kotkin said Wang was pursuing a “very ambitious” dissertation plan that included on-site research in Iran, Russia and potentially Afghanistan.

“He’s one of these kids who lives for research and ideas,” Kotkin said.

Several history graduate students described Wang as a respected scholar but declined to go into detail, citing the sensitivity of the case. The history department’s chairman, Keith Wailoo, emailed students on Monday asking them to refer news media inquiries to the school’s communications office.

One student and friend of Wang’s, who requested anonymity after Wailoo’s email, said Wang was “very driven” to succeed, working hard to learn Persian to read source material in its original form.

An official at Iran’s interests section in Washington, the country’s de facto diplomatic outpost in the U.S. capital, declined to comment in detail on Wang’s case, referring questions to Iran’s United Nations mission, which did not respond to a request for comment.

After high school in Beijing, Wang studied in China and India before moving to the United States, according to a lecture he gave years ago.

He graduated from the University of Washington in 2006 and earned a master’s degree at Harvard University, where he traveled to Uzbekistan and Tajikistan for research.

In 2008-09, Wang worked at a law firm in Hong Kong through Princeton in Asia, a program that arranges fellowships in Asia for U.S. residents.

“For better or worse, he still can’t tell you what exactly he has been studying in the many years that have passed,” a biographical note on Princeton in Asia’s website said. “What he does know is that his dream is to walk the ancient Silk Road from Xi’an to Rome one day.”