A British-Iranian dual national has been arrested in western Iran, according to his family.
The wife of Kameel Ahmady, a social anthropologist, said he was taken into custody on Sunday from their home without a reason being given.
Mr Ahmady has researched female genital mutilation and child marriage in Iran, among other subjects.
Another British dual national, Nazanin Zaghari-Ratcliffe, has been in Iranian custody since 2016 over spying claims.
Earlier this year, the UK foreign office advised all dual nationals against all travel to Iran because of the risk of arbitrary detention.
The new alleged arrest comes as high tensions, caused by oil tankers seizures, continue between the two countries.
Professional websites in Mr Ahmady's name identify him as "British-Iranian originally from Kurdistan". His LinkedIn profile says he studied at a number of UK universities, including the London School of Economics and Political Science (LSE).
A spokesman for the Kurdistan Human Rights Network, who reported his arrest, said Mr Ahmady has lived in Iran for many years.
Officials in both countries are yet to confirm he has been taken into custody.
In an interview with BBC Persian, his wife Shafaq Rahmani alleged security agents came to the couple's house and "took away documents, including his ID card".
She said a local judicial official later confirmed a one-month temporary detention order had been issued against Mr Ahmady.
"They have not provided any information about the reason for the arrest or the charges against Kameel," Ms Rahmani wrote on Instagram.
Iran does not recognise dual nationality and there are no exact figures on the number of detainees who are also foreign nationals.