Security forces launched a raid on a suspected hideout in a remote part of Assam state , home to myriad separatist insurgent groups.
"Based on specific information we raided the KPLT hideout and a firefight broke out in which we managed to neutralise six militants , including two of their top leaders," local police chief Debajit Deori told AFP by telephone.
The Karbi People's Liberation Tigers (KPLT) is fighting for an independent homeland for the Karbi tribe.
Deori said automatic weapons and ammunition, including one rifle, grenades, and "incriminating documents from the dead rebels" had been found at the scene.
One soldier was injured and was being treated in hospital.
Northeast India, linked to the rest of the country by a narrow land corridor, has seen decades of unrest among ethnic and separatist groups.
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The region is home to dozens of tribal groups and small guerrilla armies that resist rule from New Delhi.
Many are fighting for independent homelands for their tribes, and often compete against each other.
In August six gunmen of Assam's National Democratic Front of Bodoland opened fire on a busy market, killing 15 people and wounding several others.