The police said that the unprovoked half-an-hour attack took place in the Lukhambi area in the recently inaugurated Noney district.
Dikhuanang Gonmei died on the spot while his companions Jacky Kamei (35) and private teacher Thuanilung Kamei (31) suffered serious injuries.
Another person, 30-year-old Nipen Kalita, was also injured in the firing.
The convoy was carrying necessary commodities despite the three-month-long economic blockade imposed by the United Naga Council (UNC) in the state.