Two secular writers and a publisher of a slain blogger were hacked and shot in Dhaka today, police and witnesses said, the latest in a spate of attacks in Bangladesh on online critics of religious militancy.

Three unknown assailants entered the office of a publishing house and attacked the writers and the man who published slain blogger Avijit Roy's book, police official Jamal Uddin said.

The attackers locked their victims inside the office before fleeing the scene, he added. They were rushed to a hospital and two of them were in critical conditions.

In February, Islamists radicals killed Roy, 43, a US citizen of Bangladeshi origin and a critic of religious extremism. They seriously injured his wife and fellow blogger, Rafida Bonya Ahmed.

The publisher had filed a complaint with police after being threatened with death on Facebook following the attack on Roy, his friends said.

Since then, four bloggers have been hacked to death in the Muslim-majority nation of 160 million people.

Bangladesh has also been rocked by a series of unusual attacks in recent weeks, which has seen two foreigners shot dead and a bombing at a Shi'ite shrine in Dhaka that killed two people and wounded dozens.