Wang, a graduate student in history, vanished in Iran several months ago where he was doing research for a doctoral thesis.
"I have been having trouble accessing Tehran's archives and libraries", Wang had said in the 2015-2016 annual report of the British Institute of Persian Studies, a nonprofit organization based in London.
Mr Wang is certainly not the first US citizen to be jailed in Iran - although all of the other current detainees are joint US-Iranian nationals.
The US State Department did not identify its jailed citizen, but accused Iran of fabricating national security-related charges to detain Americans and other foreigners.
The U.S. State Department has not provided details on the case but called on Tehran to immediately release "all U.S. citizens unjustly detained in Iran".
The person who owns the nationality of both the U.S. and another country had snooped into Iran to gather documents and intelligence, Gholamhossein Mohseni Ejeie, spokesman for Iranian judiciary, told the reporters. "He was in Iran last summer exclusively for the objective of doing scholarly research on the administrative and cultural history of the late Qajar dynasty in connection with his PhD dissertation". While remaining USA sanctions have slowed economic gains promised by the accord, signs that worldwide interest in Iran is growing have disturbed some hardliners, who foresee their power waning.
MH17 memorial opens in Amsterdam on the third anniversary of disaster
The European Union foreign affairs chief, Federica Mogherini, called for worldwide cooperation in the hunt for the perpetrators. It's three years since Malaysian Airlines' Flight MH17 from Amsterdam was shot down in eastern Ukraine , killing 298 people.
The name of the U.S. citizen has still not been revealed and it will be done only after the appeals court approves the sentence.
At least three other Americans are thought to be imprisoned in Iran although the number could be higher.
The big news from the crime blotter for Iranian citizens over the weekend was the arrest of recently re-elected President Hassan Rouhani's brother, Hossein Fereidoun.
Iran marked the two-year anniversary of the nuclear deal on July 14. You also mentioned that Wang Xiyue has American citizenship.
The conservative-dominated judiciary has clashed with Mr Rouhani, who has sought to ease social restrictions and release political prisoners.
Mr Ejehi may also have been referring to Iranian-American art gallery manager Karan Vafadari, who was detained along with his Iranian wife previous year.
A Chinese-born United States dual national was sentenced to ten years in prison by Iranian authorities who accused him of spying for Washington.
"He was in Iran last summer exclusively for the goal of doing scholarly research on the administrative and cultural history of the late Qajar dynasty in connection with his PhD dissertation", said spokesman Daniel Day.