The video, sent by the NDFB militants and was being aired by television channels since last night, showed a 16-year-old girl lying slumped on the ground in a pool of blood in the presence of her parents and residents of Dwimugri village under Runikhata police station in the district.
Government spokesman and Industries minister Pradyut said a probe would be ordered into the killing by militants of the National Democratic Front of Bodoland (Songbijit).
The government would also take action against any policeman found guilty of dereliction of duty, he said.
The girl was suspected to have been killed a day after five NDFB(S) militants were killed in an encounter with security forces on August 20.
An NDFB(S) militant claimed in the video that the girl was killed for being 'an informer' and it was a warning to others.