A U.S. Navy veteran has been held in Iran on unspecified charges since July, when he was seized while visiting the Islamic republic, media reports said, citing his family and a former Iranian prisoner.
Michael White, 46, of California was arrested when he was visiting his Iranian girlfriend, his mother told The New York Times on January 7.
The U.S. State Department said it was "aware of reports" of the detention but did not provide further details, citing privacy considerations.
White’s imprisonment could further escalate tensions between Washington and Tehran, longtime foes.
Tensions have been high since U.S. President Donald Trump pulled Washington out of a landmark nuclear deal with Iran and reimposed crippling economic sanctions against Tehran last year.
At least five Americans have been sentenced to prison in Iran on espionage-related charges. Another U.S. citizen has been missing in Iran for more than a decade.
White's mother, Joanne, said that her son had been set to return from Iran via the United Arab Emirates on July 27, but never boarded his flight.
Three weeks ago, State Department officials told her that White was being held at an Iranian prison.
She said her son had visited Iran “five or six times” to see an Iranian woman she described as his girlfriend.
White’s incarceration was also reported on January 7 by Iran Wire, an online news service run by Iranian expatriates.
Iran Wire's report was based on an interview with a former Iranian prisoner who was quoted as saying he had met White at Vakilabad Prison in the city of Mashhad in October.
The prisoner, identified as Irvar Farhadi, was briefly held at the same facility as White in Mashhad, Iran Wire reported.
Farhadi told Iran Wire that White had met an Iranian woman online and traveled to Iran several times to see her.
On his third visit, when White and his girlfriend were about to fly to Turkey, he was arrested at Hasheminejad Airport in Mashhad, Farhadi said.
White is among several Americans being held by Iran. Among them is Xiyue Wang, a Princeton University student who has been given a 10-year sentence for espionage. He was arrested in August 2016 while conducting research for his dissertation on Iran's Qajar dynasty.
Both Wang and the university deny the claims.
Baquer Namazi, a retired UNICEF official, and his son Siamak, an Iranian-American businessman, were sentenced in 2016 to 10 years in prison for spying and cooperating with the U.S. government.
The charges were denied by the family and dismissed by U.S. authorities.
Bob Levinson, a former Federal Bureau of Investigation agent, vanished on Iran’s Kish Island in 2007 while on an intelligence mission. Tehran has said it has no information about his fate.
In January 2016, Iran released four Americans as part of a prisoners swap, including Jason Rezaian, The Washington Post's Tehran bureau chief, Saeed Abedini, a pastor from Idaho, and Amir Hekmati, a former Marine from Flint, Michigan.
In exchange, the United States released several Iranians held on sanctions violations.