Five paramilitary troopers, including a major and a captain, were killed in an ambush by separatists on Monday in Manipur, officials said.
A defence spokesperson said heavily armed militants of the outlawed United National Liberation Front (UNLF) attacked a convoy of the paramilitary Assam Rifles near Samtol village in Chandel district, about 120 km south of Manipur state capital Imphal.
"UNLF militants opened indiscriminate fire with automatic weapons on the convoy in which two Assam Rifles officers, a major and a captain, and three troopers were killed," the Assam Rifles commander said.
The UNLF is a rebel group fighting for an independent homeland for the majority Metei community in a state of 2.4 million people.
The militants fired from a hilltop as the convoy snaked through a mountainous terrain while the Assam Rifles personnel were on a routine patrol in the area, bordering Myanmar.
"There was no reaction time as the militants were in an advantageous position and fired a volley of shots," the official said.
The Assam Rifles are engaged in anti-insurgency operations in Manipur.
Police and paramilitary troopers have since begun a massive combing operation in the thickly forested area after the attack.
"In all probability the militants might have sneaked into bases inside Myanmar," the official said.
There are about 20 militant groups active in Manipur with demands ranging from secession to greater autonomy.
More than 10,000 people have lost their lives to insurgency in Manipur during the past two decades.