Four councillors were also injured yesterday during a discussion on installing high mast lights in the city.
"The attack was pre-planned and the incident cannot be trivalised.Stern action will be taken against those behind the attack", Vijayan told reporters here after visiting the mayor at the medical college hospital here.
Prasanth, who is undergoing treatment, alleged that some outsiders also took part in the violence, which was led by BJP councillors.
Meanwhile CPI(M) state secretary Kodiyeri Balakrishnan and Congress leader V M Sudheeran visited the mayor at the hospital.