The victim was identified as Abdul Basit Babul, son of Abdul Jabbar of Bagbari area of the municipality and former convener of municipality unit of Jubo League.
Suja Mamun, officer-in-charge of Chhatak police, said they did not receive the body as he died on way to MAG Osmani Medical College Hospital.
Some of the injured were admitted to the same hospital, while others received treatment at Chhatak Upazila Health Complex and Sunamganj General Hospital, he added.
Arifuzzaman, upazila nirbahi officer of Chhatak, said the two groups, one based on Qaumi madrasa and the other followers of a spiritual leader of Fultali, were supposed to arrange the mahfil. At one stage, disagreement over some issues brought the two groups to a conflicting situation on Sunday evening, he added.
Both the groups locked in a clash around 2:30pm yesterday despite efforts by the police and local administration to ease the situation.
Additional police force was needed to disperse the groups after around an hour, the UNO added.
Harun-Ar-Rashid, superintendent of police of Sunamganj, said the law enforcers brought the situation under control by firing rubber bullets and gas.