Unidentified assailants have hacked to death Bangladeshi writer Avijit Roy and seriously injured his blogger wife Rafida Ahmed Banna.

Police said the couple came under assault near at Dhaka University around 9:30pm on Thursday.

Witnesses said they were on a rickshaw returning from a book fair when two attackers stopped it, dragged them onto the footpath and started hacking them.

They were rushed to the Dhaka Medical College and Hospital where doctors declared Avijit dead during an emergency surgery.

Islamist zealots have been threatening Avijit, a bioengineer and a naturalised US citizen, for his active campaign against Islamist radicals.

Avijit has been a regular bdnews24.com columnist and the founder of popular blog Mukto-mona.

Avijit had suffered a deep gash on his head during the assault and Banna lost a finger and suffered cut wounds.