Xiyue Wang’s conviction comes at a particularly tense time for U.S.-Iranian relations. ((Friend of Xiyue Wang via AP))

An American scholar jailed in Iran for espionage is “linguistically gifted” and had “unbounded intellectual curiosity” in the pursuit of his doctorate at Princeton University, his adviser said Monday, adding to a still-emerging portrait of the graduate student whose 10-year sentence was announced by Iranian authorities the previous day.

Xiyue Wang, 37, was detained last August while researching the Qajar dynasty for his dissertation, Princeton University said Sunday. His arrest, however, was not made public until this past weekend, when the verdict was announced.

Wang, who is married and has a son, was accused of using his status as a researcher to send Iranian documents to the U.S. government and Western universities, according to a report from the official news agency of Iran’s judiciary. His trial was apparently conducted in secret. The verdict can still be appealed, a spokesman for the judiciary said.

“He is innocent of all the charges. In Tehran, Wang collected documents that were 100 years old,” said Stephen Kotkin, Wang’s adviser.

He went on to say that Wang was interested in predominantly Muslim areas across Eurasia, particularly during the late 19th and early 20th centuries. The Qajar dynasty ruled the late Persian Empire from 1785 to 1925.

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“He’s deeply interested in that region,” Kotkin said, adding that Wang, who was born in Beijing, speaks Chinese, Persian, Russian and Pashto. He arrived at Princeton in the fall of 2013 to begin his doctoral studies in history, according to Daniel Day, a spokesman for the university.

Wang, whose travel was financed by Princeton and other academic fellowships, is the latest foreign national to be arrested by Iranian security services and convicted in closed-door proceedings, often on vague charges and without access to a lawyer, human rights groups say.

Iran’s judiciary, which answers to the country’s supreme leader, is a stronghold of Iranian conservatives opposed to the country’s rapprochement with the West. Under the current system, prosecutors regularly lack evidence and punishments are harsh, including against political dissidents and those accused of national security offenses.

A number of foreigners, including U.S. citizens and dual nationals, are still believed to be in Iranian jails, and they have been used as bargaining chips in domestic power struggles and negotiations with world powers.

In Iran, “once an issue is politicized at this level, then it’s not going to be just the legal system that is the ultimate arbiter of what happens to the case,” said Alex Vatanka, senior research fellow at the Middle East Institute in Washington.

Analysts have pointed to what they say is an ongoing rivalry between Iran’s conservative judiciary and the moderate president, Hassan Rouhani, who was reelected by a landslide in May on promises of social and political reform. The arrest and conviction of an American embarrasses Rouhani, who has courted Western countries to invest in Iran.

“Wang’s arrest sends a message to Iranian dual nationals abroad and to Iranian civil society at home that hard-liners are in full control of the ship of the state, and they can arrest anyone they wish, regardless of their dual nationality or affiliation with a U.S. Ivy League school,” said Nader Hashemi, director of the Center for Middle East Studies at the University of Denver.

It “also undermines Rouhani’s plan for global integration and warmer relations with the West,” he said.

Iran’s judiciary accused Wang of attempting to create a digital catalogue of documents from the national archives and other libraries. Wang, it alleged, managed to digitize some 4,500 documents, according to the Mizan news agency, which is linked to the judiciary. Those documents would serve as resources for “English and American centers of subversion,” including the State Department, Harvard and Princeton universities, and the British Institute for Persian Studies, the report said.

Mizan also published a quote from Wang that was featured in the British Institute’s 2015-2016 annual report, in which he praised the institution for facilitating his access to academic centers in Iran.

“Wang admits his mission,” the Mizan report said, adding that the quote had been used as evidence in the case against him.

But Kotkin said that Wang had planned to travel to Russia to continue his research as part of a fellowship he had won.

“So he undertook the normal practice of any PhD student,” Kotkin said. “To photocopy or scan documents he didn’t have time to read in country. Then he’d get to it later.”

According to Suzanne Maloney, a senior fellow and expert on Iran at the Brookings Institution, the arrest of foreign and dual nationals “is kind of a consistent tactic that Iran has used.”

“This is just a system that views individual foreigners who come to the country, particularly people with some language capabilities, as inherently suspect,” she said. “When it comes to the security services, they view these kind of engagements with an incredible degree of paranoia.”

Carol Morello, Susan Svrluga and Mary Hui in Washington contributed to this report.