A fast-track court in Bangladesh sentenced two former students to death on Thursday for the 2013 murder of an online critic of religious militancy, lawyers said.

Rajib Haider, an architect and blogger, was hacked to death near his house in the capital, Dhaka, in February 2013, having led a popular movement demanding the death penalty for Islamist leaders accused of atrocities in Bangladesh's 1971 war of independence.

This year, four more bloggers and a publisher have also been killed in Bangladesh amidst a rise in Islamist violence in which liberal activists, members of minority Muslim sects and other religious groups have also been targeted.

The court sentenced two former university students charged with Haider's murder to death, said state prosecutor Mahbubur Rahman, one of whose whereabouts were not known.

Six other people were sentenced to jail terms, he said, including Jasim Uddin Rahmani, who police say is the head of the banned militant group Ansarullah Bangla Team, who was sentenced to five years in prison.

The al Qaeda-inspired Ansarullah Bangla Team has not claimed responsibility for Haider's death, but the group has said it was behind subsequent attacks on the four bloggers and a publisher this year.

Defence prosecutor Faruk Ahmed, who represented the eight men sentenced on Thursday, said his clients would appeal to the Supreme Court.