Iranian President Hassan Rohani has called the acid attacks against women "inhumane deeds" and ordered law enforcement officials to find those responsible.
Between four and eight women have had acid thrown on their heads since mid-October in the central city of Isfahan.
The women are believed to have been attacked for violating the Islamic dress code.
Most suffered horrific burns to their faces and eye damage.
Rohani on October 25 called for Iran's Interior and Justice ministries along with the secret service to quickly arrest those behind the attacks.
The Interior Ministry previously announced that four men had been arrested in the case.
The attacks led to hundreds of people protesting in Isfahan on October 22.
A large protest also took place in Tehran.
Vice President Massoumeh Ebteksr visited some of the acid victims in hospital.