At least three men riding a motorbike Sunday killed the wife of a police superintendent who led drives against Islamist militants and drug cartels in southeastern Bangladesh, police said.

Police do not know who is responsible for killing Mahmuda Khanam, but they're not ruling out militant groups, said Iqbal Bahar, the police commissioner in the city of Chittagong, where the attack took place.

No one immediately claimed responsibility for the killing.

The attackers stabbed and shot Khanam in the head as she waited with her son for a school bus, Bahar told reporters.

Khanam's husband, Babul Akter, had led a number of raids against Islamic militant groups, especially the banned outfit Jumatul Mujahedeen Bangladesh, Bahar said.

Paritosh Ghosh, a senior police official in Chittagong, said authorities were collecting video footage from closed circuit cameras at the scene.

"We do not rule out involvement of any militant groups or drug cartels," Ghosh said, adding that Akter had led a number of operations against both.

Bangladeshi authorities say suspected Islamist militants have attacked and killed a number of people in recent years, including atheist bloggers, publishers, teachers and activists, and minority groups and foreigners.

The Islamic State group has claimed responsibility for some of the attacks, according to SITE Intelligence Group, but authorities have denied that IS has a presence in the country.

Bangladesh is a Muslim-majority nation of 160 million people, but is governed by secular laws based on British common law.