The Imam was among those killed when the powerful lightning bolt hit the flimsy tin and thatch building at Saraswatipur village in the northeast some 200 kilometres (125 miles) from the capital Dhaka late on Friday.
About 35 people from the village, which is in the lake district of Sunamganj, were holding prayers known as taraweeh, offered during the Muslim holy month of Ramadan, when the lightning struck, police chief Bayes Alam said.
“All 13, including the Imam, died on the spot. The bodies and faces of some of the victims were burnt,” Alam told AFP, adding that at least 15 people were injured, including six who were hospitalised.
The locals had turned the room into a mosque because access to the village’s more substantial concrete-roofed mosque had been made difficult due to heavy rains in recent weeks that have swollen the Saraswati river.
Lightning is a major threat in Sunamganj, home to some of Bangladesh’s biggest lakes. Most incidents occur during the monsoon season between June and September when the district receives a huge amount of rainfall.