Assam on Saturday sounded a maximum security alert, deploying Army, police and paramilitary soldiers in vulnerable areas ahead of Tuesday's Independence Day celebrations even as the toll from an overnight landmine explosion went up to six.
An injured police commando died at a hospital on Saturday morning, officials said.
A convoy of three police vehicles was on a routine patrol near Pangeri village in Tinsukia district, 550 km east of Guwahati, when militants suspected to be from the outlawed United Liberation Front of Asom (ULFA) triggered a remote controlled landmine.
"Five commandos died on the spot and another who was critically wounded succumbed to his injuries at a hospital early Saturday," Absar Hazarika, district magistrate of Tinsukia district, said.
The Tinsukia district police chief, who was travelling with the convoy, was not wounded as the brunt of the explosion was borne by the last of the three vehicles carrying the commandos.
"The vehicle was blown to pieces with most of the bodies mutilated beyond recognition," Hazarika said.
In neighbouring Manipur, security forces on Friday shot dead three rebels belonging to the outlawed United National Liberation Front (UNLF) and wounded two more in a gun battle.
"We were able to recover two AK-47 assault rifles and a huge cache of ammunition from the dead rebels," Army spokesman SD Goswami said.
At least a dozen rebel groups in the northeastern states of Assam, Manipur and Tripura have called a general strike to boycott the Independence Day.
Separatist rebels in the three states stepped up violence over the weekend, killing at least 15 and wounding close to 50 others in a wave of bombings and attacks on civilians and security forces.
Militants in the insurgency-hit northeast have for years been boycotting the Independence Day and Republic Day celebrations to protest New Delhi's rule over the vast region rich in oil, tea and timber.
The run-up to the events has always been violent, with rebels striking vital installations including crude oil pipelines, trains and road and rail bridges, besides targeting soldiers.
More than 30 rebel armies operate in the northeastern states, their demands ranging from secession to greater autonomy and the right to self-determination. More than 50,000 people have lost their lives to insurgency in the northeast since independence in 1947.