Bangladesh has faced a series of attacks on liberal bloggers, university teachers and members of religious minorities over the past year.
Bangladesh's security force arrested four members of Jamaat-ul-Mujahideen (JMB) on Thursday, including a regional leader of the banned group blamed for the Islamist attack on a cafe in Dhaka in which 22 people were killed, mostly foreigners.
The Rapid Action Battalion (RAB) raided an apartment on the outskirts of the capital Dhaka and arrested the group's southern region leader and three other members, including a medical student, said RAB spokesman Mizanur Rahman Bhuiya.
"They will be interrogated intensively to understand if they had any connection with the cafe attack," he told Reuters.
A huge quality of ammunition, weapons, bomb-making materials and jihadi books have been recovered from the house, which was used for training recruits, Bhuiya added.
Five Bangladesh militants, most from wealthy, liberal families, stormed an upmarket restaurant on July 1 and murdered customers, before they were gunned down. The majority of victims were foreigners from Italy, Japan, India and the United States, before they were gunned down.
The attack, claimed by Islamic State, marked a major escalation in the scale and brutality of violence aimed at forcing strict Islamic rule in Bangladesh, whose 160 million people are mostly Muslim.
Bangladesh has faced a series of attacks on liberal bloggers, university teachers and members of religious minorities over the past year. The government says home-grown militant groups are behind the attacks.