DHAKA: Bangladesh's elite security force Tuesday arrested three suspected Islamist militants including a British citizen who police said was the "main planner" of the murders of two prominent atheist bloggers.

Rapid Action Battalion (RAB) spokesmen said they had arrested Touhidur Rahman, 58, and two other "active members" of Ansarullah Bangla Team, which was banned in May over a spate of killings of bloggers.

"We've arrested them in the capital today. We can confirm that Rahman is a Bangladesh origin British citizen. He is the main planner of the attacks on Avijit Roy and Ananta Bijoy Das,” Major Maksudul Alam of the RAB told AFP.

Four secular bloggers were killed in Bangladesh in the past six months. These include Avijit Roy and Ananta Bijoy Das.

This began when their photographs appeared on a new Facebook page registered under the name Ansar-BD. The post also said, "There are three anti-Islamic poets and three organisers of bloggers. They are the enemy of Islam. We should do whatever it takes."

Avijit Roy had founded a popular Bengali-language blog, Mukto-mona, or Free Mind, in which articles on scientific reasoning and religious extremism featured prominently.

“He was a free thinker. He was a Hindu but he was not only a strong voice against Islamic fanatics but also equally against other religious fanatics,” Baki Billah, a friend of Roy and a blogger, told Independent TV station.

The attack on Roy took place late Thursday when he and his wife Rafida Ahmed, who was seriously injured in the attack, were returning from a book fair at Dhaka University.

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Das was “an atheist and wrote blogs for Mukto-Mona,” a website which used to be moderated by Avijit Roy, Imran Sarker, head of a Bangladeshi bloggers' association, told AFP.

Attackers wearing masks hacked Ananta Bijoy Das to death with machetes in Sylhet city at around 8.30 am this morning, deputy commissioner of Sylhet police Faisal Mahmud told AFP.

Das' murder came just a week after Al Qaeda in the Indian Subcontinent (AQIS) claimed responsibility for the deadly attack on Roy.

Read more: Third secular blogger hacked to death in Bangladesh

Most secular bloggers have gone into hiding, often using pseudonyms in their posts, and at least seven have fled abroad, according to Canada-based atheist blogger Farid Ahmed, who has helped several of them.

Bangladesh is officially a secular country, but more than 90 percent of its 160 million people are Muslim.