Iranian state media published a photo purportedly of Sharmahd.
Tehran accuses the US-based pro-monarchy organization, Kingdom Assembly of Iran, of conducting attacks and sabotage in Iran, including an April 2018 terror attack in Shiraz that killed 14 people and injured 215 others.
The U.S. State Department did not immediately respond to a request for comment.
It remains unclear how the US-based accused was arrested. The group reportedly took responsibility for the attack.
Golsan discharged its cargo of food and medical supplies at the Venezuelan northern port of La Guayra on June 21 to supply the Iranian supermarket.More news: What C.J. Mosley's decision to opt out means for the Jets
It did not elaborate on where or when the leader of the opposition royalist group known as the Kingdom Assembly of Iran, or Tondar (Farsi for Thunder), was detained. The group's founder disappeared in the mid-2000s. An alleged Iranian government operative who allegedly tried to hire a hit man to kill Sharmahd disappeared in 2010 before facing trial in California, likely having returned to Iran.
While it was not clear how Iran captured Sharmahd, its operatives are known for using family members and tricks to lure exiles back to Iran or to Tehran-friendly countries.
A 2010 USA diplomatic cable from London later published by WikiLeaks shows that a Voice of America commentator said that same operative earlier had been in contact with him.
Sharmahd last appeared in an online livestream video December 29, according to his group's website, speaking in Farsi while sitting in a black chair in front of a black background. The website said he is Iranian-German and lived in Germany before moving to Los Angeles in 2003.
Iran's Foreign Ministry spokesman Abbas Mousavi reacted to the news by criticizing the US for allowing Sharmahd and others to live in America.More news: Netflix’s The Kissing Booth 2 Ending Explained
The Iranian foreign ministry said in a statement the USA "must be held accountable for backing this terrorist group and other groups and criminals responsible for sabotage, armed and terrorist operations [.] from within the United States and shedding the blood of Iranian citizens".
In a statement, the Iranian Intelligence Ministry said it had dealt a "heavy and serious blow" to the group. The group is also believed to be responsible for the 2010 bombing assassination of Iranian nuclear physicist Masoud Alimohammadi.
The supermarket, called Megasis, has been established with the goal of boosting the production and export of Iranian commodities.
In January, a USA drone attack killed a top Iranian general in Baghdad.More news: 50 new COVID-19 cases in BC, 2 in Northern Health