According to police, the incident was sequel to a by-poll in a panchayat ward which the LDF had won.
Four persons had been taken into custody in connection with the incident, they said.
The LDF candidate defeated an independent backed by the Popular Front's political arm SDPI.
Chief Minister Oommen Chandy and Home Minister Ramesh Chennithala said police had been asked to tracked down the culprits without delay.
"We cannot allow these kind of incidents to repeat. We should not allow anybody to take law into their hands," Chandy told reporters in Thiruvananthapuram.
The SDPI and IUML leaders, however, distanced themselves from the incident.
The incident sparked widespread condemnation from across the political spectrum as Malayalam TV channels beamed visuals of the attack.
