Four activists of Islami Chhatra Shibir, the student affiliate of Jamaat-e-Islami, were detained from Mirsarai upazila in Chittagong ahead of the opposition's upcoming 60-hour hartal.
Sariful Islam, 21, Imamul Islam, 19, Nurul Islam, 40, and Firoz Khan, 26, were detained from separate areas of the Jorargonj area.
Jorargonj police station Officer-in-Charge Mohammad Iftekhar Hasan said they were held for plotting subversive activities during the upcoming hartal.
A case was lodged with Jorargonj police in this regard, the OC added.
The BNP-led 18-party alliance, of which Jamaat-e-Islami is a key member, has called yet another 60-hour shutdown throughout the country, demanding the installment of a caretaker government.
The recent 60-hour shutdown resulted in the loss of at least 15 lives.