The arrests are believed to have taken place in the capital city Tehran, and in four other cities: Karaj, Rasht, Orumiyeh, and Aligoudarz during the month of July.
The exact number of arrests are not known, but at least 51 people were taken into custody, with some later released on bail, the organisation says. They say the number of people detained could be as high as 70.
The organisation believes this marks a clear shift in policy, after very few publicly reported arrests of Christians so far this year.
Mansour Borji, Article18’s advocacy director, commented, ‘The reason for this sudden surge in nationwide arrests of Christians is not clear at this stage.