No casualty was reported in the medium-intensity explosion in the complex.
The miscreants, who came in a two-wheeler, fled taking advantage of the absence of proper street lights, the officer said.
The incident came two days before the scheduled visit on April 23 of President Pranab Mukherjee in Imphal to inaugurate a war memorial monument in connection with a historical event.
CorCom, a conglomeration of various banned outfits of the state, has issued a call for boycotting the visit of Mukherjee.
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