DHAKA: A prominent US blogger, known for his writing against religious fundamentalism, has been hacked to death by unidentified attackers in Bangladesh's capital, police said Friday.

The attack on Avijit Roy, a Bangladesh-born US citizen, took place late Thursday when he and his wife Rafida Ahmed, who was seriously injured in the attack, were returning from a book fair at Dhaka University.

It was not known who was behind the attack, but Roy's family and friends say he was a prominent voice against religious fanatics and received threats in the past.

No groups have claimed the responsibility.

The local police chief, Sirajul Islam, told The Associated Press that the assailants used cleavers to attack Roy and his wife, who is also a blogger.

“Several attackers took part in the attack and at least two assailants hit them directly,” Islam said, adding that two blood-stained cleavers were found after the attack.

Roy had founded a popular Bengali-language blog, Mukto-mona, or Free Mind, in which articles on scientific reasoning and religious extremism featured prominently.

Anujit Roy, his younger brother, said Roy had returned to the country earlier this month from the US and was planning to return there next month.

Similar attacks have taken place in Bangladesh, a Muslim-majority nation of 160 million people but ruled by secular laws, in the past.

Investigators have said religious fanatics were behind those attacks. In 2013, another blogger, Ahmed Rajib Haider, who also spoke out against religious fanatics, was killed by unidentified assailants near his home in Dhaka.

And in 2004, Humayun Azad, a prominent writer and a teacher of Dhaka University, was seriously injured in an attack when he was returning from the same book fair, which is an annual event.

Baki Billah, a friend of Roy and a blogger, told Independent TV station that Roy had been threatened earlier by people upset at his writing.

“He was a free thinker. He was a Hindu but he was not only a strong voice against Islamic fanatics but also equally against other religious fanatics,” Billah said. “We are saddened. We don't know what the government will do to find the killers. We want justice,” he said.

Activists protest blogger’s murder

Hundreds of protesters gathered in Dhaka on Friday to denounce the murder Dr Avijit Roy.

The demonstrators, including teachers, publishers and fellow writers, met near the spot where Avijit Roy, founder of Mukto-Mona (Free-mind) blog, was attacked by unknown assailants as he returned home from a book fair with his wife on Thursday evening.

They chanted slogans including “We want justice” and “raise your voice against militants”.

But the atheist writer's family said he had received numerous threats from Islamists before his death, and Friday's rally is expected to draw hundreds of Bangladeshis concerned about the rise in Islamism in their country.

Roy, a US citizen, is the second Bangladeshi atheist blogger to have been murdered in two years and the fourth writer to have been attacked since 2004.

“The attack on Roy and his wife Rafida Ahmed is outrageous,” said Imran H. Sarker, head of a Bangladeshi bloggers' association.

“We strongly protest this attack and are deeply concerned about the safety of writers. “Hardline Islamist groups have long demanded the public execution of atheist bloggers and sought new laws to combat writing critical of Islam.

Police have launched an investigation and recovered the machetes used in the attack, which they compared to that on atheist blogger Ahmed Rajib Haider in 2013.

Haider was hacked to death by members of a little-known Islamist militant group, triggering nationwide protests by tens of thousands of secular activists.

Shiblee Noman, the assistant commissioner of Dhaka police told AFP that “the pattern of the killing appeared to be the same that of previous attack on a celebrated writer.”

“It seems it was carried out by reactionary fundamentalist group. “Noman also said police were investigating a tweet by the pro-Islamist group Ansar Bangla Seven that appeared to celebrate Roy's murder.

“Target Down here in #Bangladesh,” the group tweeted from the @AnsarBn7 handle.

'Threatening' emails

Roy's wife, who is also a blogger, was moved to a clinic for further treatment on Friday. The writer's father Ajoy Roy said he had received a number of “threatening “emails and messages on social media from hardliners unhappy with his writing.

Roy had written about 10 books, including the best-selling “Biswasher Virus” (Virus of Faith), as well as his blog, which championed liberal secular writing in the Muslim-majority nation. The Center for Inquiry, a US-based charity promoting free thought, said it was “shocked and heartbroken” by the brutal murder of Roy.

“Dr. Roy was a true ally, a courageous and eloquent defender of reason, science, and free expression, in a country where those values have been under heavy attack,” it said in a statement.

Roy's killing also triggered strong condemnation from his fellow writers and publishers, who lamented the growing religious conservatism and intolerance in Bangladesh.

Pinaki Bhattacharya, a fellow blogger and friend of Roy, said one of the country's largest online book retailers was being openly threatened for selling Roy's books.

“In Bangladesh the easiest target is an atheist. An atheist can be attacked and murdered,” he wrote on Facebook.

After Haider's death, Bangladesh's hard-line Islamist groups started to protest against other campaigning bloggers, accusing them of blasphemy and calling a series of nationwide strikes to demand their execution.

The secular government of Prime Minister Sheikh Hasina reacted by arresting some atheist bloggers.

The government also blocked about a dozen websites and blogs to stem the fervour over blasphemy, as well as stepping up security for the bloggers.

Bangladesh is the world's fourth-largest Muslim majority nation with Muslims making up some 90 per cent of the country's 160 million people.

A tribunal has recently handed down a series of verdicts against leading Islamists and others for crimes committed during the war of independence from Pakistan in 1971.