Bangladesh has banned an Islamist militant group thought to be behind the brutal murders of three atheist bloggers, a government official has confirmed.

"The [junior home minister] today signed a government order, outlawing the militant organisation Ansarullah Bangla Team," ministry spokesman Sharif Mahmud told AFP today. The move follows a police call for the group to be banned after ABT were implicated in the killings.

The murders, which all took place earlier this year, have sparked international outrage and large protests in Bangladesh. Avijit Roy was the first to be killed; he moderated the Mukto-Mona website, which he described as "an Internet congregation of freethinkers, rationalists, sceptics, atheists, and humanists of mainly Bengali and South Asian descent." He also authored a number of books including The Philosophy of Disbelief and The Virus of Faith, and was outspoken against religious fundamentalism and extremism.

Roy had previously received several death threats from Islamist groups, and was eventually hacked to death by men with machetes and knives in Dhaka on 26 February. His wife, Rafida Bonya Ahmed, lost several fingers in the incident, but survived. She later called on the Bangladeshi government to bring the perpetrators to justice. "I do not believe that simply catching the killers will be enough. I urge the government to address terrorism and stop a legal culture of impunity, where writers can be killed without the killers being brought to trial," Ahmed said in a statement. "I urge the world to recognize what has happened and join us in this demand for justice."

However, in March, 27-year-old blogger Washiqur Rahman became the second secular blogger to be murdered, also in Dhaka. Like Roy, he was hacked to death. A third blogger who wrote for Mukto-Mona, Ananda Bijoy Das, 32, was murdered by men with meat cleavers and machetes earlier this month.

Human Rights group Amnesty International has condemned the murders, which is says have been facilitated by government failures. Though Bangladesh is officially a secular country, more than 90 per cent of its residents are Muslim, and hardline Islamists are gaining influence.

"Some of these killings have been claimed by extremists – but they have been facilitated by the official failure to prosecute anyone responsible," said Abbas Faiz, Amnesty International's Bangladesh Researcher following the death of Das.

His murder "again shows that Bangladesh is not doing enough to protect critics of religious intolerance, or to prosecute their attackers," Faiz added.

"The prevalent impunity for all these cases continues to send a message that such attacks are tolerated by the authorities. Ending impunity and ensuring protection for those at risk must be a priority for the Bangladeshi authorities."