The incident took place last night on the New Dhansiri bridge road in Dimapur, they said, adding the bomb was made of gelatine sticks and packed with sharpnels.
Two passers-by were injured in the blast, police said.
They were rushed to a hospital, while one who was critically injured, was referred to Guwahati, they said.
Four vehicles passing the area were damaged in the blast, police added.
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