Leaders and activists of the BNP clashed with police officers during the party's march in Pirojpur on Tuesday.
Pirojpur Sadar police station OC Abir Mohammad Hasan said seven policemen were injured in the clash and have been admitted to Pirojpur District Hospital.
The incident took place on the road in front of the local fire service office around noon.
The police have arrested six people in connection with the clash.
Pirojpur BNP Convener Alamgir Hossain said 10-12 activists of the BNP and its affiliates were injured after police baton-charged them.
Meanwhile, OC Abir said BNP leaders and activists attacked police with sticks and threw bricks at them during the party's march on Circuit House Road in the city.
Police later brought the situation under control.
Additional forces have been deployed, the OC said, promising legal action in this connection.