Under which act, National Liberation Front of Twipra (NLFT) was banned since the year 1997?

Since the year 1997, National Liberation Front of Twipra (NLFT) has been banned under the Unlawful Activities (Prevention) Act,1967 and has been involved in violence, from its camps across the international border in Bangladesh. It has been responsible for violent activities, including 317 insurgency-related incidents( where 28 security forces personnel and 62 civilians lost their lives) during the period from 2005 to 2015. Peace talks with NLFT were initiated in 2015&there it has not been involved in any violence activity by NLFT since 2016.