Three members of a family were seriously burned in an explosion at a house in Dudhmou village of Bharpasha Union in Bakerganj, Barishal, on Monday morning.
The explosion occurred at the home of Shah Alam Howlader.
The injured were identified as his wife, Hanufa Begum, their daughter, Eti, and their grandson, Fahim.
They were taken for treatment and referred to Sher-e-Bangla Medical College Hospital in Barishal.
Divisional Commissioner Khalil Ahmed said the three were later sent to Dhaka for further treatment on doctors' advice because their condition was serious.
Jamal Talukdar, Shah Alam's son, said the blast came from an object in sacks of sand beside the house and that the family did not know how it got there.
Additional Superintendent of Police Masum Billah said preliminary examination suggested the object may have been a locally assembled IED-type, bomb-like device.
Police said teams inspected the site and collected samples or other evidence.
Bakerganj police station officer-in-charge Adil Hossain said investigators were working to establish the type of explosive used and identify anyone involved.
Masum Billah said no one had been detained as of Monday evening and that legal action was being prepared.