The detainees are Mufti Saiful Islam, Salim Mian, Junayed Hossein and Ahmad Sohayel.
Rapid Action Battalion (RAB) arrested four members of banned militant outfit Ansar Al Islam from the capital's Gabtali and Savar's Aminbazar areas last night.
The detainees are Mufti Saiful Islam, 34, hailing from Manikganj; Salim Mian of Brahmanbaria, Junayed Hossein of Munshiganj and Ahmad Sohayel of Sunamganj district.
Additional Deputy Inspector General (DIG) Mozammel Haque, commanding officer of RAB-4, said this at a press conference in the RAB's Kawran Bazar media centre today.
He said Ansar Al Islam team were planning for target killing of those who opposed the establishment of Islamic Khilafat in the country.
After the primary interrogation, the elite force came to know that Mufti Saiful was currently teaching at a madrasa in the capital's Badda area.
He was a member of Harkat-ul-Jihad-al-Islami in his student life. After the Huji was banned, he turned to the Ansar Al Islam. He is an active activist of the militant outfit.
Salim Mian, who lives in the capital's Hazaribagh area, came Dhaka from Brahmanbaria in 2004.
Salim works at a lift company. In 2013, he met Saiful and then joined Ansar Al Islam.
Earlier, Junayed was a member of the Huji. Later, he became a member of the Ansar Al Islam. He also teaches at a madrasa in Savar's Hemayetpur.
Sohayel is a madrasa student. He joined the team through online three years ago.
"The Ansar Al Islam members use online apps to communicate with each other and upload videos to attract youths," said Additional DIG Mozammel.
The group collected fund from its members for running the organisation, he added.
"In target killing, the militant group usually use chapati (a local sharp weapon)," he said.