The ultras exploded an improvised explosive device (IED) at Kashungabout 11.15 am, police said.
The deceased was identified as Havildar Rohit.
The three injured, who are yet to be identified, were airlifted by a helicopter to the Leimakhong Army Hospital in Imphal, they said.
A large number of central forces' personnel and police commandos rushed to the area to conduct search operations.
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