The Rapid Action Battalion (RAB) detained six suspected robbers with arms and ammunition in the Bay of Bengal late on Friday.
The detainees are Nezam Uddin, 22, Md Shakil, 24, Md Sajjad, 35, Md Sujan, 24, Md Manik, 32, and Omar Farooq, 21.
Three locally-made guns and 11 rounds of ammunition were recovered from their possession, said RAB-15 chief Major Sheikh Yusuf Ahmed.
Acting on a tip-off, a RAB team carried out a raid in the Sonadia channel in Maheshkhali, as the group of robbers had been preparing to rob a fishing trawler, he said.
The six will face legal action in this connection, the RAB official added.