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.