India has launched an operation in its northeastern region to find the militants who killed 20 soldiers and wounded a dozen others.
Officials say the insurgents in Manipur state ambushed an army troop convoy Thursday using rocket-propelled grenades and bombs.
Officials say the army has been given shoot-to-kill orders to use against the militant hideouts in the area.
Several rebel groups have claimed responsibility for the assault.
Manipur has struggled for years with an armed insurgency.
Prime Minister Narendra Modi called the attack "mindless" and "very distressing."
"It is a very sad thing and we sympathize with them and the whole country is with them. But they are brave people who have sacrificed themselves for the country," said Ajit Doval, India's National Security Advisor.