DHAKA: Police detectives in Bangladesh's capital arrested two suspected militants in the killing of a secular blogger last week in the fourth such deadly attack this year.

Dhaka Metropolitan Police spokesman Muntasirul Islam said that Saad-al-Nahin and Masud Rana, suspected members of Ansarullah Bangla Team, a group blamed for some of the previous attacks on bloggers, were arrested Thursday evening by the detective branch, which has been handling the case rather than regular police.

Local media reported that Nahin was arrested in 2013 on a charge of attempted murder in an attack on blogger Asif Mohiuddin, who was injured. Nahin was freed on bail but was supposedly being watched by detectives.

Last Friday, at least four men posing as tenants entered an apartment building and hacked to death the 28-year-old Niladri Chottopadhay Niloy. The blogger's wife, Asha Moni, filed a murder case against four unnamed persons.

Also read: Bangladesh vows to 'hunt down' secular blogger's killers

Friends of Niloy, who also goes by an online name of Niloy Chowdhury, said he had received several threats that prompted him to remove all his photos from his blog. They said he had a Facebook account in which he criticised religious extremism at home and abroad.

The family and friends said Niloy had sought police protection after he was threatened, but police asked him to leave the country for his safety.

Hours after the killing, Ansar-al-Islam, which intelligence officials believe is affiliated with Al Qaeda on the Indian Subcontinent, sent an email to media organisations claiming responsibility for the attack. The authenticity of the email could not be independently verified.

The United States has expressed its concern over the killing, while the United Nations called for Bangladeshi authorities to ensure accountability and prevent such violence.

In February, Bangladeshi-American Avijit Roy was hacked to death on the Dhaka University campus while walking with his wife. Two others were attacked and killed in March and April, one in Dhaka and another in the northeastern city of Sylhet. Investigations into the previous cases made no headway.

Also read: Third secular blogger hacked to death in Bangladesh