Police in Bangladesh have arrested two more suspected members of a banned militant group thought to be behind the slaying of a secular blogger in the fourth such deadly attack this year.

Dhaka Metropolitan police official Mahbub Alam said Kausar Hossain Khan, 29, and Kamal Hossain Sardar, 29, were arrested in raids in the capital city late Thursday and that they were suspected members of the Ansarullah Bangla Team blamed for attacks on atheist bloggers and writers.

The arrests follow the arrests two weeks ago of two other suspects — Saad-al-Nahin and Masud Rana — for involvement in the killing of the 28-year-old blogger Niladri Chottopadhay Niloy.

Alam said the latest arrests were a result of interrogations of the two.

Niloy was hacked to death on Aug. 7. His wife, Asha Moni, filed a murder case against four unnamed persons, and the seriousness of the case meant the investigation was handed to the Detective Branch of the police from the regular police.

Police would not provide more details about Khan and Sardar but said they were out on bail after being accused of attempted murder in an attack on another blogger, Asif Mohiuddin, two years ago. Mohiuddin has since fled for Germany.

Niloy was known to his friends as an atheist blogger whose online name is Niloy Chowdhury. His family and friends said he has criticized radical Islamists at home and abroad, and had sought police protection after receiving threats. The police asked him to leave the country for his safety, they said.

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. U.N. Special Rapporteur Heiner Bielefeldt is scheduled to visit Bangladesh from Monday to assess the state of freedom of religion and belief in the South Asian country.

In February, Bangladeshi-American blogger 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 those cases have made no headway.