"Mamata Banerjee has been a great 'Himayati' (protagonist) of communal harmony," Kumar said after coming out of a state Cabinet meeting.
Kumar said he did not have details of the incident as he was busy with his work in Bihar.
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But all efforts should be made to maintain social and communal amity in the country, he added.
Kumar's support to his West Bengal counterpart comes at a time when she is battling BJP's blistering attack over violence in Malda.
Kumar enjoys a close relationship with Mamata Banerjee — who had attended his swearing-in ceremony in November last year in Patna.
Violence had broken out at Kaliachak in Malda district on December 3 over an alleged remark by a BJP leader. Protesters had set fire to a police station and damaged vehicles.
The West Bengal CM had said there was no communal tension in the area and described the incident as the fallout of an issue between BSF and the local people.