Police in Bangladesh said Thursday they had arrested two members of a banned group for their alleged involvement in the killing of a blogger last week — the latest attack on critics of religious extremism in the Muslim-majority nation.

Two suspected members of an outlawed group known as the Ansarullah Bangla Team were arrested in Dhaka for alleged links to the killing of 40-year-old blogger Niloy Chatterjee, Senior Police Official Mahbub Alam said.

Secularist writers in Bangladesh have been targeted in recent years. Chatterjee, an advocate of secularism who was best known by his pen name, Niloy Neel, was killed by attackers armed with machetes in his apartment in the capital city of Dhaka on Friday.

Chatterjee focused his writing on human rights, minorities and a war crimes tribunal set up to punish those who allegedly collaborated with Pakistani soldiers during Bangladesh’s war of independence from Pakistan decades ago.

Bangladesh says more than 3 million people were killed and 200,000 women were raped during the nine-month war, which ended in December 1971.

Chatterjee's death marked the fourth such killing of an online critic of religious extremism in less than six months, spurring calls by human rights groups for a swift and thorough investigation.

While the government has tried to crack down on groups seeking to make the South Asian nation of 160 million people a Sharia-based state, critics say the government has shown indifference to the recent attacks on defenders of secularism and free expression.

Most secular bloggers have either gone into hiding or have fled abroad, and they often use pseudonyms in their posts. Activist groups say they fear that hit squads are targeting the bloggers and have access to their full names and addresses.

"Niloy was an activist of the pro-liberation platform. He was killed because there is no justice in the country," Imran Sarker, the head of a network of activists and bloggers, said last week after Chatterjee's death.

Al Jazeera and wire services