An atheist blogger has been hacked to death in Bangladesh, the third blogger to be killed in the country this year, as writers say Islamist militants are working their way down a hitlist.

Ananta Bijoy Das, a 33-year-old banker, was attacked by a group of masked men on Tuesday morning in the northeastern city of Sylhet, according to police. Friends and family of the blogger told VICE News that he had been online shortly before he was killed, and had left home to run an errand. He was attacked with machetes, first with blows to the head then to the rest of his body.

Fellow bloggers told VICE News Das wrote posts and was an administrator for the blog Mukto-mona (Free Thinker), a website promoting rationalism that was founded by US-Bangladeshi blogger Avijit Roy, who was also hacked to death in February. Das wrote posts for Mukto-mona focusing on science and evolution, as well as sometimes criticizing Islam and Hinduism.

Blogger Shubhajit Bhowmik said that Das was also a member of a local organizing body for the Gonojagoron Moncho protest movement, which campaigned in 2013 for harsher sentences for a group of Islamist leaders convicted of war crimes that took place during the 1971 war for independence from Pakistan. Another friend told the Guardian newspaper that Das was the editor of a quarterly magazine called Jukti (Logic) and headed a Sylhet-based science and rationalist council.

Imran H Sarker, head of Blogger and Online Activists Network, told VICE News there was a culture of impunity for the murder of bloggers in Bangladesh — where more than 90 percent of the population is Muslim, though the country is officially secular. "Besides the murderers, the state is also to blame for the killings," he said, adding a protest would take place in the capital of Dhaka on Tuesday evening.

Fellow writers told AFP that Das had been on a hitlist drawn up by militants who were behind the murder of Roy. Das's murder happened almost 10 days after a group known as al Qaeda in the Indian Subcontinent (AQIS) claimed responsibility for Roy's murder of Avjit Roy alongside other similar murders in Pakistan and Bangladesh, in a video released on May 2.

In the video, called From France to Bangladesh: The Dust Will Never Settle Down, AQIS leader Maulana Asim Umar said his group killed the bloggers because they insulted Islam.

Roy was an atheist and had written a book titled The Virus of Faith, which likened religious extremism to an infectious disease_. _He had come to Bangladesh in February to promote the book during an annual literary festival in Dhaka when he was killed on February 26.

Umar claimed AQIS was also responsible for the deaths of the "blasphemers" Mohammad Shakil Auj, an Islamic scholar shot dead in the city of Karachi in Pakistan last year, the Pakistani blogger Aniqa Naz, who was reportedly killed in a road accident in Pakistan in 2012, and Bangladeshi blogger Rajib Haider, who was killed in a machete attack in Dhaka in February 2013. Roy and Haider were also involved in the Gonojagoron Moncho movement.

After Haider's murder in 2013, the Bangladesh police arrested several suspects, who they claimed were members of a violent Bangladeshi Islamist group called Ansarullah Bangla. The group was also blamed for a number of similar assaults in which the victims survived, including another in January 2013 on prominent blogger Asif Mohiuddin.

After the video was posted earlier this month, Dhaka police chief Muhammad Habibur Rahman told Reuters: "We have to investigate whether [Ansarullah Bangla] is working as the branch of al Qaeda."

Days after Roy's murder, Bangladeshi police arrested Farabi Shafiur Rahman, an Islamist blogger who had threatened Roy online a number of times, although he is not thought to be linked to the extremist group.

In February, an FBI team visited Bangladesh to assist local murder investigators. VICE News has learnt from Bangladesh police sources that they are currently waiting on the DNA test reports to arrive from the FBI before a significant breakthrough can be made in the case.

In an interview with Reuters published this week, Avijit Roy's wife Rafida Ahmed Bonna — who lost a thumb during the attack on her husband — said his murder "was well planned, choreographed — a global act of terrorism."

She said she was shocked that no one from the Bangladeshi government had got in touch with her. "It's as if I don't exist, and they are afraid of the extremists," she said. "Is Bangladesh going to be the next Pakistan or Afghanistan?"

A spokesman at the Bangladesh Embassy in Washington said he did not know why no one from his government had yet to contact Ahmed, who, like her late husband, is a dual Bangladeshi-US citizen.

"We are shocked at the killing of Avijit Roy and have taken all measures to find the culprits responsible for this heinous act," spokesman Shamim Ahmad told Reuters. "Bangladesh is committed to fighting and ending extremism in all its forms."