At least 12 atheist bloggers have fled Bangladesh after a spate of gruesome killings by Islamists, the Deutsche Welle reports.

All are outspoken atheists and fear they will targeted by extremist Islamists after a hit list of 84 bloggers was pubilshed online. 

Four atheist bloggers have died so far this year in Bangladesh where more than 90 per cent of the population is Muslim. However bloggers claim that 100,000 among Bangladesh's population of 160 million are atheist.

Despite Bangladesh's constitutional guarantee of free speech, atheism remains a taboo.

There is a widely held but mistaken perception that atheists are "anti-religious," said Ali Riaz, a professor of politics and government at Illinois State University.

Avjit Roy was killed in Dhaka in February. Local media reported that he and his wife were dragged from their rickshaw into a sidealley where he was hacked to death by assailants with machetes. 

After this attack the government did nothing. It was thought they feared mass demonstrations by Islamists who believe the bloggers defamed Islam and the Prophet Muhammed.

After six months, three more deaths and intense international pressure, the Government finally made some arrests. Three suspects were taken into custody on 10 September including the chief of Ansarullah Bangla Team, an outlawed militant group which claimed responsibility for the recent killings.

"The investigations of the killing of bloggers are proceeding at full pace. The police have arrested some suspected killers, and a Dhaka court has already started trial of one of the murder cases," information minister Hasanul Haq Inu said.

However he also alluded to a possible clampdown on free speech in order to combat blasphemy.

While "no one can harass an atheist for his beliefs, writing or doing something to defame a religion is a punishable crime in our country," he said.

"We won't allow any such act."