DHAKA, Bangladesh - 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.

Separately, the Islamic State group claimed responsibility for the killing of a Christian man Sunday in northwestern Bangladesh.

Police said they did not know who was responsible for killing the police superintendent's wife, Mahmuda Khanam, but they were not ruling out militant groups, said Iqbal Bahar, the police commissioner in the city of Chittagong, where the attack took place.

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.

Authorities in Muslim-majority Bangladesh 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.

In the other attack on Sunday, unidentified men hacked to death a Christian man in northwestern Bangladesh's Natore district, police said.

Family members found Sunil Gomes lying in a pool of blood after the attack in his grocery shop, which is close to a church and a Christian neighbourhood, said Monirul Islam, a local police chief in Natore.

The Islamic State group-linked Amaq News Agency said IS was responsible for the attack.

Minority groups in Bangladesh have said that people from the country's Christian, Hindu and Buddhist communities have received threats from suspected Islamist groups. At least 12 bishops received threats in various forms ahead of last Christmas.

News from © The Associated Press, 2016