The demand came in the wake of Chief Minister Mukul Sangma recently accusing the ANVC-B militants of indulging in a criminal conspiracy with the ISI to create communal tension.
"The Chief Minister should immediately ask for an NIA probe to investigate into the matter so that appropriate action can be taken instead of offering mere lip service," NPP spokesperson James K Sangma said in a statement here.
At least 24 ANVC-B militants were arrested from West Garo Hills district last month for their alleged involvement in killing migrant labourers in neighbouring Assam.
Sangma said, "The statement made by the CM which is of an extremely serious nature, bears significance since it is coming from the executive head of the state who is privy to intelligence reports and the veracity of this allegation cannot be contested."
Stating that the security agencies in the state were not adequately equipped to deal with it, the NPP said the NIA was the appropriate agency to handle with such serious matters.