"Two of the suspects are now in our custody...They are Ansarullah Bangla Team (ABT) members," a police spokesman told PTI of the arrests in connection with Niloy Chakrabarty Neel's murder at his flat here last Friday.
The police spokesman identified the detained suspects as Saad-al-Nahin and Masud Rana and said they were under surveillance as suspected ABT members.
The arrests came amid criticism of police after Inspector General Shahidul Haque asked the bloggers not to "cross the limit" or write anything which hurts religious beliefs of others.
"Neel wrote nothing which could have hurt anyone in that way...Actually the extremist Islamists are trying to create space for themselves using religion," Neel's friend and fellow blogger Meraj Mohamad said.
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He said Neel earlier sought police protection but was advised to leave the country.
Mohamad said 40-year-old Neel later gave a foreign address in his Facebook account in an effort to divert the assassins.
Ansar-Al-Islam, also known as the Ansarullah Bangla Team which is the Bangladesh chapter of the Al-Qaeda in the Indian Sub-Continent, claimed responsibility for Neel's killing.
Neel was an activist of a platform -- the Ganajagaran Mancha which waged a massive campaign for the capital punishment for war criminals who carried out atrocities siding with the Pakistani troops in 1971.
The murder of Neel, who was brutally killed inside his flat here with 14 hack wounds found on his body, is the fourth such brutal death in the country. Machete-wielding masked men in May hacked to death 33-year-old Ananta Bijoy Das, a secular blogger, in Sylhet city.
Assailants in February had killed 45-year old Avijit Roy, a Bangladesh-born US national, here while his wife narrowly escaped the attack.
The US had condemned the hacking to death of Neel as a "cowardly murder" and underlined the need to work together to counter violent extremism.