Police said 34-year-old Rajesh's left hand was chopped off in the attack which took place around at 9 pm last night.
An investigation has been launched and search is on for assailants, they said.
BJP state president Kumanam Rajasekharan alleged that the CPI-M was behind the attack, a charge denied by the district leadership of the Left party.
The BJP has called for a state-wide hartal today, the state BJP chief said.
Police are maintaining a strict vigil and have clamped prohibitory orders for three days from July 28 after BJP's Kerala unit office here was vandalised and the house of CPI-M state secretary Kodiyeri Balakrishnan's son Bineesh Kodiyeri was attacked.
Earlier, 10 people, including four from the student and youth wing of the CPI-M, had been arrested in connection with the violence in the city.