The publisher of an atheist writer killed earlier this year by suspected Islamists was hacked to death in Bangladesh Saturday, hours after two secular bloggers and another publisher were also attacked.

Both attacks in the capital Dhaka -- the latest in a wave of violence targeting secular activists -- followed the same pattern, with the assailants attacking the men with machetes and cleavers, leaving them in a pool of blood and padlocking their offices from the outside as they left, police said.

Faisal Arefin Dipan, 43, the owner of Jagritee publishers, was killed in his third-floor office in central Dhaka, his father Abul Kashem Fazlul Haq, a noted intellectual and writer, told AFP.

"I rushed to his office at Aziz Market and broke the padlock. And I saw him lying upside down in a massive pool of blood. They slaughtered his neck. He is dead," he said.

Haq told AFP that he became worried about his son after he heard of the earlier attack that left publisher Ahmedur Rashid Tutul, 43, and bloggers Ranadipam Basu, 50, and Tareq Rahim, 30, who is also a poet, severely injured.

"He published the books of Avijit Roy. They also attacked other publishers of Roy but only my son died," Haq said.

Atheist blogger Roy was hacked to death outside a book fair in February -- the first death of five in a wave of violence against secular writers in Bangladesh this year.

Dipan was a friend of Roy as and published his bestseller, Bishwasher Virus (The Virus of Faith).

In the first incident on Saturday, three armed men posing as shoppers entered the offices of Shuddhaswar publishing house at 3pm (0900 GMT), police said.

"Once inside, they started hacking Tutul, the publisher of Roy, and secular bloggers Basu and Rahim with machetes and cleavers indiscriminately and shot at Rahim from a firearm," said Dhaka police deputy commissioner Wahidul Islam.

"They then padlocked the office from the outside and left the three in a pool of blood. Our officers broke the door and rescued them after getting emergency calls," he said.

The three men were in hospital and one was in a critical condition, Islam said.

Al-Qaeda in the Indian Subcontinent (AQIS) claimed responsibility for the attacks via Twitter.

"These two atheist-apostates have published books that have attacked the honour of the Prophet (Mohammed) and mocked Islam", the group said in a Bengali statement posted using the Twitter handle Ansar al Islam.

Police spokesman Muntashirul Islam said officers had seen the statement, but could not confirm whether the Al-Qaeda branch was responsible for attacks.

"We're investigating whether the claim is credible. So far it seems the attacks were pre-planned and carried out by organised miscreants," Islam told AFP.

Police officers said both the attacks bore the hallmarks of earlier attacks on bloggers.

Tutul, who published several books by Roy, had sought police protection, saying he had received threats after the writer's murder.

"We gave him police protection. But in recent weeks he asked us to withdraw the security measure, saying his office was now secured," deputy police commissioner Islam said.

Hundreds of activists held an impromptu march in Dhaka Saturday evening, criticising the government for failing to protect the country's secular writers.

"We're stunned. One after another secular writers and bloggers have been silenced and murdered. Yet the government has failed to protect them," said Imran Sarker, who heads a secular bloggers group.

Rights group Amnesty International also asked the government "to do everything possible to find the attackers", saying it has "reason to believe that many other lives are now at risk."

"The situation in Bangladesh is becoming increasingly dangerous for those brave enough to speak their own minds," the group said.

Bloggers said in the wake of recent murders about a dozen secular writers have fled the country following threats from the Islamists and the latest attacks would prompt more to do so or go into hiding.

Police have said the banned local Islamist militant group Ansarullah Bangla Team (ABT) were behind the previous attacks, which were also claimed by Al-Qaeda in the Indian Sub-continent.

Tensions are high in Bangladesh following the bombing of Dhaka's main Shiite shrine last weekend, which killed one person and wounded dozens more.

The attack further raised concerns for minorities living in the mainly Muslim but officially secular nation.