"They were arrested on a secret tip off and they appeared radical Islamists as interrogations are underway," a police official told PTI.
Ten of the 21 arrested yesterday night are students of Bangladesh University of Engineering and Technology (BUET), while others are enrolled in several other universities and medical colleges, he said.
Police said they suspected the students assembled at the restaurant to form a new Islamist party. However, an official said none of the arrested have admitted to be members of any such outfit.
A resident of the neighbourhood said several platoons of police laid siege to the restaurant complex last night and came out with the students early in the morning.
Bangladesh has earlier banned radical Hizbut Tahrir, an extremist rightwing grouping of university students and young professionals, but its activists often try to stage quick street protests carrying banners.
