The incident came as a great embarrassment to Congress as it happened on a day the party is celebrating its formation day.
Unnithan, who resigned from the post of KPCC spokesperson yesterday, was attacked allegedly by a group of Congress workers in front of the DCC Office at Kollam when he was proceeding to attend the party celebrations.
Sudheeran wanted party workers to desist from airing their views in public and said "party is our strength and we should strengthen it."
Former Chief Minister Oommen Chandy said intolerance towards criticism should be avoided and it should be taken positively.
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Meanwhile, Muraleedharan also termed the attack on Unnithan as unfortunate. He also wanted the party leadeship to intervene and sort out the matter.
However, Unnithan alleged that "paid goons" of Muraleedharan were behind the attack.
Muraleedharan and Unnithan had sparred after the former charged that party-led UDF Opposition was not functioning as an effective opposition.