At least 20 people, including policemen, were injured in a clash between BNP activists and law enforcers at Kazir Deuri area of Chattogram city on Monday.
The clash broke out around 4pm and lasted for an hour.
BNP activists torched several vehicles near Nasiman Bhaban. Police fired several shots to control the situation.
Mohila Dal President Monowara Begum, BNP leader Akhi Sultana and 13 others were detained from the spot.
BNP Office Secretary Idris Ali said BNP activists were preparing for a peaceful rally and accused police of obstructing them and firing at them as they tried to reach BNP office.
Fifteen BNP activists were injured in the firing and 50 others were wounded during police action, he claimed.