As Iran's state TV continues to show pro-regime rallies, fears are growing for those arrested in a crackdown on anti-government protests.
More than a week of unrest that started last month saw some 22 people die, with over 1,000 detained, according to Iranian officals.
Unrest spread to more than 80 cities and rural towns as thousands of young and working-class Iranians voiced anger at corruption, unemployment and a deepening gap between rich and poor.
The protests are said to have subsided in recent days after Revolutionary Guard forces were dispatched to several provinces.
Reformist MPs claim that around 90 university students are among those being held in custody - some of whom are unaccounted for.
"It seems that the total number of detainees is around 90. Ten students from universities in Tehran and some other cities are in an uncertain position, and ... it is still unknown which body has detained them," the labour news agency ILNA quoted reformist politician Mahmoud Sadeghi as saying.
Iran has several parallel security bodies and residents say arrests are often not immediately announced.
Tehran University Vice-President Majid Sarsangi said the university had set up a committee to track the fate of students arrested during the unrest.
Concern over what has become of those detained is shared by Iranians abroad. They made their voices heard in Europe on Saturday.
As well as Paris, London and Stockholm, several hundred held a rally in front of Berlin's Brandenburg Gate, with Iranian flags, drums and banners, calling for a change in their country's government.
One of the protesters in Berlin, 18-year-old Pariya Kohandel Saleh, said her father was in jail in Iran for supporting the families of prisoners.
"Things should be good in Iran now the sanctions have been lifted, but the mullahs' pockets are bottomless and everybody knows it," she told Reuters.