Agartala, Nov 8 : The National Investigation Agency (NIA) on Wednesday arrested at least 25 people -- 21 in Tripura and 5 in Assam, for their alleged involvement in human trafficking and infiltration-related activities, an official said. A highly-placed source said that in Tripura, the arrests were made in the districts of West Tripura, South Tripura, Sepahijala and Unokoti. The arrested individuals have been taken out of the state for questioning and further legal action. Besides, five persons were also arrested in different places in Assam. The NIA and Assam Police in co-ordination with other security agencies on Wednesday conducted raids in Tripura, Assam, West Bengal and a few other states. Sources said that in February this year, a group of Rohingiyas, including women, was detained from a Guwahati-bound train from Tripura in Assam's Karimganj Railway Station by the Assam Police. After a thorough investigation, it came to light that Rohingyas and Bangladeshi infiltrators were entering India, through the India-Bangladesh border. Since then, Assam Police have increased vigilance and operations following which 450 illegal immigrants (Rohingyas/Bangladeshis) were stopped and turned back with the assistance of the Border Security Force. During the enquiries and questioning of Rohingyas and Bangladeshi infiltrators, it was revealed that the illegal migrants were facilitated in entering India through clandestine routes by touts and middlemen, who have been playing a major role in the infiltration and human trafficking, sources said. During the investigation, it was also learnt that touts exist not only on both the sides of India-Bangladesh Border but also on the mainland of the country. "Investigation revealed that a network of touts existed across India, which was a serious national security concern with inter-state ramifications," a source said, adding that Tripura and Assam are used as corridors for infiltration and human trafficking activities. /IANS