In reaction to the murder of Niladri Chattopadhyay, Amnesty International said the government must send a strong message that killings aimed at silencing dissenting voices are despicable and will not be tolerated.

"This spate of savage killings must end here. There is little doubt that these especially brutal killings are designed to sow fear and to have a chilling effect on free speech. This is unacceptable," said David Griffiths, South Asia Research Director at Amnesty International.

The online activist was stabbed to death by a group of unknown assailants at his home in Dhaka this afternoon.

Known for his secularist views, he is the fourth blogger to meet such a brutal fate at the hands of machete-wielding groups this year.

"The price for holding opinions and expressing them freely must not be death. The Bangladeshi authorities now have an urgent duty to make clear that no more attacks like this will be tolerated," David Griffiths said in a statement today.

"Thorough, effective, independent and impartial investigations must be carried out promptly to ensure that all those responsible are brought to justice in fair trials without recourse to the death penalty."

Three other bloggers were targeted in similar killings in the country since February this year – Avijit Roy, Oyasiqur Rahman and Ananta Bijoy Das.