The CPI(M) on Sunday strongly condemned the "planned" attack on its national headquarters by BJP-RSS workers and demanded their immediate arrest.
In a statement, the party politburo said the Central committee meeting of the party was in session when the attack occurred.
Four central committee members and other office staff were injured in the attack, it said. "The attackers brought stones along with them and damaged the office building and vehicles parked outside," the statement said.
"This unprovoked violence should be condemned by all political parties and such attacks can have no place in our politics. The few policemen who were there on the spot did nothing much to control the situation," it added.