Unidentified men have killed the wife of a senior Bangladeshi police officer responsible for operations against religiously motivated armed groups.

Three unidentified men stabbed and then shot Mahmuda Khanom in the head as she walked her son to a school bus stop near her home in the coastal city of Chittagong, the city's Metropolitan Police deputy commissioner Moktar Hossain said.

She was the wife of Babul Akter who has led several high-profile operations against the banned Jamaatul Mujahideen Bangladesh (JMB) group in the southeastern city in recent months.

Police said they had launched an investigation after the attack.

Q&A: Why are bloggers being killed in Bangladesh?

He had fled to Dhaka a few days ago after receiving threats. So far no one has claimed responsibility for the murder.

A nation of 160 million people, Bangladesh has seen a surge in violent attacks over the past few months in which liberal activists, members of minority Muslim sects and other religious groups have been targeted.

However, security forces or their families have not been targeted in the wave of attacks.

Also on Sunday, a Christian grocer was hacked to death near a church in northwest Bangladesh.

Sunil Gomes, 65, was killed in the village of Bonpara, home to one of the oldest Christian communities in Muslim-majority Bangladesh.

The Islamic State of Iraq and the Levant (ISIL, also known as ISIS) has claimed responsibility for some of the previous killings.

The government, though, denies the group has a presence in the country, saying homegrown groups are behind the attacks.

Source: Al Jazeera and agencies