The Improvised Explosives Device that went off at a traffic police box in Chattogram's Sholoshahar on Friday was detonated by remote control.

A separate cell of the IS-inspired militant outfit Neo JMB carried out the attack. The IED was powerful enough to kill people, officers said.

"The IED made by the outfit was equipped with a remote control circuit and battery, and they used tiny metal balls as splinters," said a high official of Counter Terrorism and Transnational Crime (CTTC) unit of Dhaka Metropolitan Police. 

But the device didn't cause massive damage because of a flaw in its design, the official said, requesting anonymity.

Moniruzzaman, additional deputy inspector general of Anti-Terrorism Unit, told The Daily Star: "Analysing data and evidence collected from the scene, we are sure that the attack was carried out by a militant outfit and it has similarities with how Neo-JMB operates.

"We did not get CCTV footage. To detect the attackers, we are now looking at their digital footprint and referring to information we got earlier from interrogating different arrestees."

Neo JMB is an ultra-radical offshoot of the banned militant outfit Jama'atul Mujahideen Bangladesh, CTTC officers said earlier.

In Friday's blast, Traffic Sergeant Arafat, Assistant Sub-inspector Atauddin, and pedestrians Jahid Bin Jahangir, Sumon and ten-year-old Nowshad were hurt.

A case was lodged with Panchlaish Police Station on Saturday night accusing unidentified persons.

Officers said the nature of the attack had many similarities with five earlier blasts in the capital and two in Khulna.

As were the cases after the aforesaid attacks, SITE Intelligence Group, which tracks online activity of jihadist organisations and white supremacists, said the Islamic State claimed responsibility for the Chattogram blast.

Police on January 25 this year claimed that they have arrested two people involved with the attack on Khulna Awami League office. On September 23 last year, CTTC claimed it arrested two others suspected of being involved with the blast in Dhaka.

A high official of CTTC yesterday said his team had dismantled two Neo JMB cells that were behind last year's attacks in Dhaka and Khulna.

"The Ameer [leader], who used to control these cells still remain untraced," he told The Daily Star, seeking anonymity.

"We suspect there are at least two or three other cells under this Ameer, and one of those cells is responsible for the latest blast."

Each of the cell has four or five members. But the cells don't maintain contact with each other, he added.

The counterterrorism unit of Chattogram Metropolitan Police (CMP) investigating the case has not been able to detect any suspect.

Deputy Commissioner Hasan Md Showkat Ali of the unit told The Daily Star: "We have interrogated several persons near the scene but no one was able to give any information about the attackers.

"We are using modern technology to find a clue."