A prominent atheist blogger has been murdered during a visit to Dhaka.
Bangladeshi-American Avijit Roy, who had travelled to the Bangladeshi capital with his wife to attend a book fair, was found covered in blood after the attack which also left his wife critically wounded.
He had received threats after publishing articles promoting secular views on science and social issues which had been criticised for being anti-Islamic.
Roy was founder of the Mukto-Mona (Free-mind) blog site which champions liberal secular writing in the Muslim-majority nation.
Local media reported that he and his wife Rafida Ahmed were on a bicycle rickshaw when two assailants stopped then and dragged them onto a sidewalk before striking them with machetes.
He is the second Bangladeshi blogger to have been murdered in two years and the fourth writer to have been attacked since 2004.
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 a probe and recovered the machetes used in the attack but could not confirm whether Islamists were behind the incident.
But Roy's father said the writer, a US citizen, had received a number of 'threatening' emails and messages on social media from hardliners.
Ajoy Roy told the news agency AFP: "He was a secular humanist and has written about ten books including his most famous 'Biswasher Virus' (Virus of Faith)".
The Center for Inquiry, a US-based charity promoting free thought, said it was 'shocked and heartbroken' by the murder.
"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, citing growing religious conservatism and intolerance in Bangladesh.
Pinaki Bhattacharya, a fellow blogger and friend, claimed 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.
Atheist blogger Ahmed Rajib Haider was hacked to death in 2013 by members of a little known Islamist militant group, triggering nationwide protests by tens of thousands of secular activists.
After his death, Bangladesh's hardline Islamist groups started to protest against other campaigning bloggers, calling a series of nationwide strikes to demand their execution, accusing them of blasphemy.
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 furore 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.