Police said Faisal Arefin Dipan, 43, was killed in his third-floor office in central Dhaka on Saturday.

"I saw him lying upside down and in a massive pool of blood…He is dead," Dipan's father and noted Bangladeshi writer, Abul Kashem Fazlul Haq, told AFP.

Blogger Imran H Sarker and medical sources confirmed Dipan's death to DW journalist Arafatul Islam.

Dipan owned Jagriti Prokashoni Publishers based at Aziz Supermarket, a hub for alternative publishers in Dhaka. He published the book, "The Philosophy of Disbelief," by slain blogger Avijit Roy, a winner of DW's 2015 Bobs award for online activism.

Roy was hacked to death outside a book fair on the Dhaka University campus in February.

Britain's High Commissioner to Bangladesh, Robert Gibson, condemned the attack on Twitter.

Bloggers attacked

Saturday's killing came just hours after a separate attack, in which unknown assailants forced their way into the office of the Shudhdhoswar publishing house and stabbed and shot two secular bloggers and another publisher.

Police said the intruders locked the wounded men inside the office and fled the scene. "We had to break the lock to recover them," local police chief Jamal Uddin Meer told Associated Press. All three men were hospitalized.

The two writers have been identified as Ranadeep Basu and Tareque Rahim. The publisher, Ahmed Rahim Tutul, had also published several books by Avijit Roy. Roy's wife Bonya Ahmed, herself a secular blogger, wrote on Facebook:

''I am speechless, don't want to cry but can't stop my tears. They hacked both of Avijit's publishers and two others. I am sure (the) Bangladeshi Government will still say that there is no hint of Islamic terrorism in the country!''

Protest

Protesters massed outside at the hospital where the victims were taken to demand the government do more to protect the country's secular bloggers. Rights group Amnesty International also called on authorities "to do everything possible to find the attackers," adding that it has "reason to believe that many other lives are now at risk."

At least four atheist bloggers have been murdered in Bangladesh this year. Those killings had been claimed by local Islamist group Ansarullah Bangla Team.

Later on Saturday, another Islamist group, Ansar al-Islam - the Bangladesh branch of Al Qaeda in the Indian Subcontinent (AQIS) - claimed responsibility for the attacks on Dipan and Tutul. The group said on Twitter that the "secular and atheist publishers" had released books by blasphemers that dishonored the Prophet Muhammad. The claim of responsibility could not be independently verified.

nm/jm (Reuters, AP, AFP)