At least 50 people were injured in a clash between BNP activists and police at Naogaon town on 30 March noon.
Witnesses and police said the clash erupted when police barred a demonstration by BNP activists in front of the party office at KD intersection.
District unit convener of BNP, Hafizur Rahman, was leading the demonstration as part of the central programme, protesting against the police attack on Hefazat-e-Islam Bangladesh activists.
Police charged baton on the demonstrators to disperse them. BNP activists retaliated by pelting brick chips at the police.
To bring the situation under control, police fired tear shells and rubble bullets. The clash continued for nearly 20 minutes, halting traffic movement around the neighbouring areas.
BNP activists left the spot soon after the deployment of reserved force of police.
Naogaon BNP convener Hafizur Rahman alleged that police charged baton and fired tear shells on BNP activists without any provocation, leaving 50 people injured.
Among the injured, Mily Akhter and Azizul were sent to Rajshahi Medical College Hospital as their conditions are critical. The rest were admitted to Naogaon general hospital, Hafizur said.
Additional superintendent of police in Naogaon, Raquibul Akter said BNP activists tried to bring out a demonstration without prior permission from the administration. Police barred the move of demonstration on a busy road.
Raquibul said that some police personnel were too injured as BNP activists pelted brick chips at them.
Preparations were underway to file a case in this regard, he added.