Members of Rapid Action Battalion arrested two suspected members of Jama'atul Mujahideen Bangladesh from a house in Elenga municipality under Kalihati upazila of the district early yesterday.
They also recovered a drone, bomb making materials and several machetes and Chinese axes from the house.
The detainees are Syed Nurul Huda, alias Masum, 30, and Syed Mazharul Islam, alias Khokon, 25, sons of late Syed Abul Hossain Chistee of the municipality.
Although the militants had been carrying out their activities at the house for long, locals did not know anything about it.
Abdul Mia, a resident of the area, said he had known the brothers, Masum and Khokon, as very polite people.
He said Masum has a medicine shop at Masinda bazar while Khokon has a computer and mobile servicing shop in Capsule Market on Victoria Road in the town.
Masum was in Malaysia for about nine years and returned to Bangladesh three years ago and started poultry and medicine business, he added.
Their father Syed Abul Hossain Chishtee, who died about two and a half years ago, was known as a pir in the area, he added.
Masum married a girl near his maternal grandfather's house at Ghatail upazila, while Khokon married the daughter of one of his father's admirers in Meherpur.
"The pir saheb was a very good man, and we are surprised to hear about the involvement of his two sons in militancy," said Rahima Begum, a resident of Masinda village.
"Masum and Khokon hardly talked with local people," said Habibur Rahman, a local fruit trader and also a neighbour of the family.
Several locals said Masum and Khokon said their prayers regularly, and zikir and religious meetings used to be held at their house.