"Terrorism and extremism are completely inimical to democracy. This incident calls for strong condemnation and those believing in democracy should be ashamed of this atrocious incident," he said.
Responding to a set of questions in party mouthpiece 'Murasoli', Karunanidhi said that encouraging terrorism and extremism will harm democracy and called for action against those involved in the attack.
He also expressed his party's sympathies with families of the victims while wishing injured Congress leader V C Shukla a speedy recovery.
While a section of the ruling class was opposed to it, Sri Lankan Defence Secretary Goabaye Rajapakse was reported to have said that Colombo cannot toe India's line on the issue.
Karunanidhi recalled that External Affairs Minister Salman Khurshid had last week asked Sri Lanka not to make any attempts to "weaken" the 13th amendment and added that in such a situation it was doubtful if elections would be held there this year as scheduled.