Police raided a house in northwestern Chapainawabganj on Wednesday night, triggering a standoff.
"We found bodies of four militants as we entered the hideout," a police headquarters spokesman told reporters in Dhaka as elite Special Weapons And Tactics unit wrapped up the security clampdown codenamed 'Operation Eagle Hunt'.
An injured pregnant woman, who is the wife of one of the slain militants, and her six-year-old daughter were brought out from the house as siege ended at the den of Neo Jamaat- ul-Mujahideen, the spokesman said.
Last month Bangladeshi police conducted series of large- scale operations against militants, in which at least 17 suspected militants were killed.
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On March 31, eight militants blew themselves up with a grenade after the security forces raided their hideout north of the Bangladeshi capital.
The official said the woman too was believed to be an operative of the banned outfit responsible for carrying out out the deadly July 1, 2016 terrorist attack on a Dhaka cafe in which 22 people, including an Indian, were killed.
Bangladesh has been witnessing a spate of attacks on secular activists, foreigners and religious minorities since 2013. The country launched a massive crackdown on militants specially after the Dhaka cafe attack.