Police have detained five people, posing as members of the Detective Branch (DB) of Police, from Motijheel area in Dhaka.
The detainees could not be identified immediately.
"A team from Motijheel police station conducted a drive in the area and detained them with firearms, ammunition, handcuffs and walkie-talkies last night [Sunday], Dhaka Metropolitan Police (DMP) Deputy Commissioner (media) Masudur Rahman said on Monday.
He said they also seized a private car in the drive.
Details regarding the matter will be disclosed in a press briefing later in the day.