The officer in-charge of the Bhanga police station and six others were wounded in the accidental fire by Awami League leader Deepak Majumdar's bodyguard during the rally in Faridpur district, police said.
"The shot was misfired from a gun in possession of Deepak Majumdar's bodyguard," said Nazmul Islam, who sustained injuries on his shoulder.
He was being treated at an area hospital.
The other injured persons have been referred to Faridpur Medical College Hospital for treatment.
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Some media reports quoting witnesses suggested that the incident happened during a scuffle between the organisers of the rally and the villagers there.
They claimed that the gun belonged to Majumdar.
Majumdar, however, has denied that the shotgun belonged to him as he "even did not join the rally".