The police detained two men on Sunday for what authorities described as suspicious movement near the Gulshan residence of Bangladesh Nationalist Party (BNP) acting chairman Tarique Rahman.
The men were identified as Md Ruhul Amin, 46, and Md Omar Faruk.
Amin, from Matlab South upazila in Chandpur, was seen taking photographs of the residence and nearby vehicles from different angles in the morning, police said.
Law and order in Bangladesh has deteriorated since the fall of the previous government leading to mob violence and political strife.