Media playback is unsupported on your device Media caption Mahfuz Sadique: "Critics say the government has failed to properly address recent attacks"

Suspected militants in Bangladesh have killed the wife of a senior police officer who is playing a leading role in investigating a spate of murders committed by Islamists, officials say.

Mahmuda Aktar was shot in the head in Chittagong in front of her six-year-old son.

Her husband, Supt Babul Aktar, is investigating the banned Islamist Jamayetul Mujahideen Bangladesh group.

Police say Mrs Aktar may have been killed because of her husband's work.

Police spokesman Iqbal Bahar said that three men stabbed and then shot her.

"She came out of her apartment to put her son on the school bus [when] suddenly three people on a bike came close to her.

"First they stabbed her and later they shot her. She died immediately.

"As Babul Aktar was involved in working against the militants we will investigate whether the militants carried out this operation."

Image copyright AFP Image caption The murders of university professors, bloggers and minority religions have triggered country-wide protests

Hardline Islamist ideology

Among those attacked over the last year are university professors, secular bloggers, gay rights activists, foreigners and members of religious minorities including Shia, Sufi and Ahmadi Muslims, Christians and Hindus.

Some of these attacks have been blamed on the JMB, which, like other militant groups in the country, dislikes anyone not prepared to embrace their hardline Islamist ideology.

Supt Aktar has led several raids on militant hideouts and investigated numerous terror-related cases in his role as the additional deputy commissioner with the Detective Branch in Chittagong, BD News 24 reported.

Image copyright EPA Image caption The body of Mahmuda Khanam Mitu was left by her killers on the streets of Chittagong before police arrived

Supt Aktar was at the forefront of a police operation in October to arrest JMB chief Mohammed Javed.

Mr Javed was killed in a grenade explosion the day after his arrest while leading police to a JMB hideout.

Home Minister Home Minister Asaduzzaman Khan Kamal said after Sunday's attack that the government was now considering providing better security for families of police officers.

"Militants have adopted this strategy to take on soft targets like families of police officers because they have been cornered," he said.

In a separate development, unidentified men hacked to death a Christian grocer in the country's north-west. Police said the motive for the killing in Natore district was unclear.

The group known as Islamic State (IS) said it had carried out the attack.

The government however has repeatedly insisted that IS does not have a presence in the country.

It has blamed more than 20 murders by suspected Islamists over the past three years on opposition parties and local militant groups.

Is extremism on the rise in Bangladesh?

Lurching from secularism to sectarian terror?

Who is behind the Bangladesh killings?

Muslim-majority Bangladesh is officially secular but critics say the government has failed to properly address recent attacks.