Sub-inspector Bikash and three constables were given first aid in the Assam Rifles camp in Noney, and later transferred to hospitals here for better medical treatment, police said.
The attack came hours after militants killed three police personnel and injured 11 others in Tengnoupal district.
Chief Minister Okram Ibobi Singh and senior ministers will inaugurate the district on Friday.
According to officials, the panic stricken tribal villagers are terrified to attend the function as the militants may strike during the event.
Additional police and paramilitary personnel have been rushed to the district to maintain law and order.
Meanwhile, tribal village authority in a statement expressed objection to the creation of the new district.
It said the tribal elders have no objection to the new district, but the word "revenue" from the nomenclature should be deleted, it said.
The Manipur Gazette in 2012 said in a report that Noney had been renamed Longmai and the nomenclature Noney was unacceptable.