Dhaka Metropolitan Police said the suspects' national ID cards and fingerprints were used to identify seven of the nine slain militants.
Those identified are - 'Abdullah' (23), Abu Hakim Nayeem (24), Motiur Rahman, Zobayer Hossain (22), Taj-ul-Haque Rashik (24), Akifuzzaman Khan (24) and Shehzad Rauf Arka.
Shehzad was a US passport holder, police said.
The youth, 'missing' since February, had been a friend of dead Dhaka cafe attacker Nibras Islam, Bdnews24.Com reported.
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Nibras had been staying in Jhenaidah with nine other youths in Jhenaidah.
Police suspect Shehzad had been with Nibras there.
Police said the nine terrorists were killed while one was captured alive during the operation codenamed 'Storm 26'.
Officers believe the nine slain extremists were part of the same group that killed 22 people during an attack on an upscale Dhaka cafe on July 1 -- an attack claimed by IS.
Police said they recovered IS' black flag and robes from the Dhaka hideout, but maintained that the extremists are actually members of the domestic Islamist group Jamayetul Mujahideen Bangladesh.
Dhaka's police commissioner Asaduzzaman Mia had said that terrorists were "highly educated".
Bangladesh is reeling from a wave of deadly attacks by Islamist extremists.
22 people, including an Indian girl, were killed and around 30 others injured by suspected ISIS militants inside a cafe in Dhaka in the worst terror attack in Bangladesh.
The government, however, maintains that the home grown militant outfit Jamaat-ul-Mujahideen was behind the attack.