Police today said the SSI Mohan was on security duty for a Public meeting being held by Dalit outfit Adhi Tamizhar Peravai in Vadivelkaran near Nagamalaipudukottai,when he saw the trio threatening people and gesticulating menacingly and warned them against it.
Though they left the spot, they came back later, picked up an argument with him and hacked him, police said, adding he has been hospitalised.
Two persons have been detained in connection with the incident and are being questioned, they said.