In a mysterious statement, Ansar al-Islam, the Bangladesh division of al-Qaeda in the Indian Subcontinent (AQIS), has condemned the killing of Mahmuda Khanam Mitu, wife of Superintendent of Police Babul Akter, US-based SITE Intelligence Group reports.

The statement came hours after the law enforcement agencies had launched a special weeklong anti-militant drive across the country.

Assailants stabbed and shot dead Mitu, who left her OR Nizam Road residence in the port city of Chittagong on foot to drop her son at a school bus pick-up location around 6:45am on June 5.

According to a report on SITE website, the militant outfit, which is infamous for its brutal style of killing people, termed Mitu's killing "impermissible under Islam".

Ansar al-Islam Calls Mahmuda Aktar's Murder Impermissible, Condemns "Ploy" to Blame Jihadists https://t.co/vrQGXv89q0

— SITE Intel Group (@siteintelgroup) June 10, 2016

The statement said it is a ploy to blame the jihadists, the SITE report added.

Police authorities in Bangladesh said Babul Akter earned militants' ire for his success in anti-militancy drive. In his reaction to the June 5 murder, Home Minister Asaduzzaman Khan Kamal said the militants aimed to morally break SP Akter by killing his wife.

The victim's husband Akter, who served as additional deputy commissioner of detective branch of CMP earlier, got promotion as superintendent of police recently and was posted at police headquarters in Dhaka, sources said.

During the investigation, the law enforcers today claimed to have detained a man who they suspect was seen in CCTV footage to be talking on mobile phone while following Mitu before her murder.

Md Shah Zaman alias Robin, who hails from Laksham in Comilla, was detained from Shital Jhorna area under Bayezid Police Station of Chittagong city, Chittagong Metropolitan Police (CMP) Commissioner Iqbal Bahar said at a press briefing today.

"We are yet to affirm whether he is that man. We will verify his identity after examining the CCTV footage more closely," Iqbal Bahar told reporters.

The CMP commissioner also said driver of a black microbus, who was detained on Wednesday, was freed as police did not find his link with the murder through verification and interrogation.

Earlier on June 8, police detained ex-activist of Islami Chhatra Shibir Abu Naser Binnu in Farhadabad area of Hathazari in Chittagong suspecting his link with the murder.