British-Iranian anthropologist Kameel Ahmady was arrested in Tehran at the weekend and taken to the notorious Evin prison, his wife said on Wednesday.
Evin prison is known for housing political prisoners, academics, artists, journalists and activists.
British-Iranian charity worker Nazanin Zaghari-Ratcliffe has been held in the women’s wing of Evin prison for much of the time since she was arrested in 2016.
Mr Ahmady's wife, Shafagh Rahmani, said her husband had not been charged with a crime and prosecutors had not disclosed the accusations.
"My husband was granted British citizenship 25 years ago but has been living in Iran in the past 15 years," Ms Rahmani told Radio Farda.
The arrest of her husband comes amid heightened tension between Iran and the UK.
Mr Ahmady’s website shows he has conducted research in a sensitive issues in Iran, including the first comprehensive study of female genital mutilation and "temporary marriages".
He has also looked into the identity of different ethnic groups in Iran and the lives of children scavenging for waste in Tehran.
Mr Ahmady has worked in Africa, the Far East, Bosnia, Turkey, Afghanistan and Iraq.
He “became interested in the everyday lives of these local populations, their traditions and customs, particularly the harmful ones, and also the effect conflict, war and poverty has had on them".
He studied at the London School of Economics and in the Netherlands, and says he has published books and papers of gender, minorities, early child marriage and "honour" killings.
The UK Foreign Office said it was aware of the reports of Mr Ahmady’s detention.
Its official travel advice warns against all travel to Iran by British-Iranian citizens, and warns that its diplomats' ability to provide consular support to those detained is "extremely limited".
"There is a risk that British nationals, and a higher risk that British-Iranian dual nationals, could be arbitrarily detained in Iran," the guidance says.
"All British nationals should consider carefully the risks of travelling to Iran.
"The Iranian authorities don’t recognise dual nationality for Iranian citizens and therefore don’t grant consular access for FCO officials to visit them in detention."
Ms Zaghari-Ratcliffe remains in jail having been convicted of espionage in 2016, a charge she denies.
Abbas Edalat, a British-Iranian academic at Imperial College London, was released last December after eight months' detention in Tehran on unspecified charges.
Relations between Tehran and London are particularly tense after the Iranian seizure of a British-flagged vessel in the Strait of Hormuz.
It came only two weeks after UK forces detained an Iranian oil tanker off Gibraltar, which appeared to be heading to Syria in breach of sanctions.
On Tuesday an official in Gibraltar rejected reports in Tehran that the Iranian ship was set to be released.
