The JD(U) leader also flayed Modi for invoking the President's message on tolerance and plurality instead of directly condemning the lynching incident.
He said Modi's comments on Thursday on maintaining communal harmony and eradicating poverty were not "strong enough" to allay apprehensions among the people.
Kumar also accused BJP of playing the communal card to divert attention away from the real issues.
"The PM should have reacted quickly. His statement was not strong enough. Instead of remaining silent, he should have reacted immediately (on the Dadri incident) to allay apprehensions and repose confidence among people," Kumar told 'Times Now'.
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At an election rally yesterday, Kumar had also accused Modi of using President Pranab Mukherjee's statement as an 'alibi' and asked him to show courage to condemn the Dadri lynching incident in 'unequivocal terms'.
Kumar had also dared him to a debate.
JD(U) is contesting the upcoming Bihar polls as part of a grand alliance with RJD and Congress, exuded confidence about their victory and asserted that the alliance would remain intact after the elections even as he dismissed suggestions of joining hands with Asaduddin Owaisi's AIMIM should such a situation arise.