Investigators have found that banned militant outfit Harkat-ul-Jihad al-Islami (Huji) was giving training to children in the guise of running a madrasa.

For this purpose, Huji had taken lease of a piece of land in a remote hilly area of Bandarban after collecting funds from sympathisers.

The Huji's "operations wing" head, Mohammad Mainul Islam alias Mahin alias Mithu alias Hasan, used to operate the training activities. Identifying himself as a "journalist", he took lease of the land, said investigators of Counter Terrorism and Transnational Crime (CTTC) unit.

Mainul had managed an identity card from a media outlet in Dhaka. He used to collect information about Huji's target using the identity.

CTTC officials claimed to have discovered the Huji training camp and learnt about its activities following the arrest of Mainul and his two associates from the capital's Sayedabad area on March 4.

The two other arrestees are: Sheikh Sohan Swad alias Boro Abdullah and Murad Hossain Kabir.

A case was filed with Jatrabari Police Station against the three under the Anti-Terrorism Act. They were remanded in custody in two phases. The thee are now behind bars.

Speaking to The Daily Star, a top CTTC official said they conducted a drive at the Bandarban "madrasa" and rescued 24 children aged between eight and 12 years from there.

Requesting anonymity, the official said they have already handed those children to their parents and guardians, mostly labourers in hilly areas.

Investigation sources said they found identities of 40 people from some documents of the "madrasa" and also during interrogation of the three arrestees. Of the 40, some allegedly joined the Huji recently while a few others provided funds.

Saiful Islam, deputy commissioner of CT investigation wing, said they have got some details about Huji by interrogating its operations wing head.

"We still have no information regarding militant or criminal activities of the 40 people," he told The Daily Star.

The 40 were under surveillance and they would be given counselling in phases, said Saiful.

According to CTTC officials, arrested Mainul was trying to brainwash the local people around the "madrasa".

Saiful said Mainul is a notorious militant. He had planned to snatch jailed militant Abu Jandal. But he was arrested by Rapid Action Battalion in 2015 before he could implement the plan.

Walking out of jail on bail a few years ago, Mainul again started re-organising the activities of Huji. He contacted jailed militants using different techniques, said investigators.

Mainul was tasked with re-organising the Huji activities, forming a full-fledged Shura committee, ensuring funding from financiers and members of the outfit, recruiting operatives on a large scale, and collecting ammunition and bomb-making equipment, added investigators.

A CTTC high official, who interrogated Mainul, said he admitted using the media identity card as it helped him move freely and get access to different places, including offices of law enforcement agencies.

It helped Mainul collect information on Huji's targets and draw plans for sabotage, said the official requesting anonymity.

"We are trying to learn whether Mainul managed journalist ID cards for other Huji members. We have identified the person who issued the card to Mainul. We are now trying to checkwhether that person, member of a reputed journalists' club, provided the card to Mainul knowingly or unknowingly," added the official.