The brother of President Hassan Rouhani has been detained and an unnamed US citizen sentenced to 10 years behind bars for "infiltrating" the country.
The identity of the US citizen did not directly match the background of anyone known to be held in the Islamic republic.
Mr Rouhani's brother, Hossein Fereidoun, was taken into custody over allegations of financial impropriety and is eligible for bail but has not paid it yet, said judiciary spokesman Gholamhosein Mohseni Ejehi.
Mr Fereidoun is a close confidante of the moderate president, a cleric who changed his surname to Rouhani, meaning "spiritual," after joining the seminary decades ago.
He was part of the negotiating team that sealed Iran's landmark nuclear deal with world powers in 2015, winning the country relief from international sanctions in exchange for limits on its atomic energy program.
The deal was unpopular with Iranian hard-liners, whose influence runs deep within the judiciary. They saw the nuclear deal as giving too much away in exchange for too little.
Mr Fereidoun has long been a target of hard-liners, who accused him of misdeeds including money laundering and misappropriation of government funds.
The unproven allegations were a flashpoint during the May presidential election, with the president's hard-line challengers demanding that the judiciary investigate accusations against Mr Fereidoun.
Mr Rouhani trounced his nearest opponent to secure a second term in office in the first round of voting.
The US citizen whose sentence was also announced faces 10 years in prison.
"It was verified and determined that he was gathering (information) and was involved in infiltration," said Mr Ejehi although he did not elaborate on what specific charges led to the conviction, which he said could be appealed against, or say when the verdict was handed down.
The suspect was described as a dual national of the United States and another foreign country.
The US state department was not immediately able to provide any details on the case.
"The Iranian regime continues to detain US citizens and other foreigners on fabricated national security-related changes," it said in a statement.
"We call for the immediate release of all US citizens unjustly detained in Iran so they can return to their families."
The US does not maintain formal diplomatic relations with Tehran and warns its citizens, particularly dual nationals, that they risk arrest or being barred from leaving Iran.
Mr Ejehi could have been referring to Nizar Zakka, a US permanent resident from Lebanon who advocates for internet freedom.
He lives in Washington DC and has done work for the US government. He went missing in Iran in September 2015.
Permanent residents do not hold American citizenship, but they have the right to live in the US indefinitely and are eligible to apply for it after living in the country for several years.
But Mr Zakka was already known to have been sentenced to 10 years behind bars last year after being accused of espionage-related charges.
Mr Ejehi may also have been referring to Iranian-American art gallery manager Karan Vafadari, who was detained along with his Iranian wife last year. They have yet to be convicted of a crime.
Other American dual nationals who have been taken into custody and remain in Iran include Iranian-American businessman Siamak Namazi and his 81-year-old father, Baquer Namazi.
They are both serving 10-year sentences for "cooperating with the hostile American government."
Another Iranian-American, Robin Shahini, was released on bail last year after staging a weeks-long hunger strike while serving an 18-year prison sentence for "collaboration with a hostile government."
Still missing is former FBI agent Robert Levinson, who vanished in Iran in 2007 while on an unauthorised CIA mission.