A prominent Bangladeshi-American blogger known for speaking out against religious extremism was hacked to death as he walked through Bangladesh's capital with his wife, police said Friday.

The attack Thursday night on Avijit Roy, a Bangladesh-born US citizen, occurred on a crowded sidewalk as he and his wife, Rafida Ahmed, were returning from a book fair at Dhaka University. Ahmed, who is also a blogger, was seriously injured. It was the latest in a series of attacks on secular writers in Bangladesh in recent years. A previously unknown militant group, Ansar Bangla 7, claimed responsibility for the attack, Assistant Police Commissioner S.M. Shibly Noman told the Prothom Alo newspaper. Roy "was the target because of his crime against Islam," the group said on Twitter.