The trio, belonging to the National Socialist Council of Nagaland (Isak-Muivah), were arrested from near a college with one 9 mm pistol, 3 live rounds and Rs 10,000 in cash, an official release said.
They were handed over to Imphal West police station.
Following the arrest, local people demonstrated in front of the Assam Rifles in the town, and stopped vehicular movements there, the release said.
Services of inter-state buses, taxis and trucks were affected due to the protest.
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