Officials say a two-hour gun battle Saturday resulted after a convoy of security personnel and election workers was ambushed by suspected rebels firing from a hill in the thick jungle of Manipur state in the far east of India.
The area where the attack took place held the final phase of local assembly elections on Friday. The ambushed contingent - which included members of the India Reserve Battalion, were apparently transporting polling materials, including electronic voting machines.
The executive director of the Institute for Conflict Management, Ajai Sahni, says the number of casualties inflicted by the suspected insurgents is unusual for a single encounter.
"This was an election security party which was returning which was ambushed and then an engagement resulted. There are very frequent incidents [with] regular fatalities, but not of this scale," he said.
Military officials say the insurgents were well armed and fired automatic weapons.
There are nearly 20 rebel groups active in Manipur, which borders Burma.
The largest of those groups, the United National Liberation Front, opposed the elections. It is calling for a referendum to determine whether Manipur should secede from India.
Insurgent violence in India's five restive northeastern states in the past decade has claimed more than 15,000 lives.