At least three Ganajagaran Mancha organisers were injured when crude bombs were blasted minutes before their programme in Bogra town on Saturday morning.
Police said the miscreants were among the crowd posing as Ganajagaran Mancha activists. Some policemen were also slightly hurt at scene.
The incident took place during a nationwide blockade of the BNP-led 18-party alliance.
A human chain programme protesting the recent actions of Pakistan regarding executed war criminal Abdul Quader Molla was due in Satmatha area around 11am.
About six crude bombs exploded in the area minutes before the programme was set to begin.
Those injured were: Mancha Bogra unit coordinator Rahman Helal, Bangladesher Samajtantrik Dal Bogra Convener Saiful Islam and Mancha activist Dulal Kunda.
Saiful Islam was taken to Mohammad Ali Hospital for treatments.
Bogra police spokesperson and Assistant Superintendent Gaziur Rahman said the miscreants were in the crowd posing as Mancha activists.
Some policemen also sustained minor injuries from the blasts, he said.