At least four soldiers were wounded in a powerful landmine explosion triggered by separatists in Arunachal Pradesh, military officials said on Thursday.
The blast on Wednesday in Chokham village in Lohit district, 600 km from state capital Itanagar, was suspected to be carried out by militants of the outlawed United Liberation Front of Asom (ULFA), said an army official.
"A group of soldiers was travelling on a convoy when one of the vehicles was hit by the landmine, injuring four soldiers - two of them critically," an army commander said.
"The soldiers were on a routine patrol when the incident took place. The area is remote and located in a densely forested area," he added.
The attack is seen as retaliation to the killing of eight ULFA militants by army soldiers earlier this month in the same district.
"They (ULFA) are getting frustrated with the heavy reversals against them in recent months," the official said.
A rebel group fighting for an independent homeland since 1979 in Assam, ULFA has recently set up bases in adjoining Arunachal Pradesh, following a massive military offensive against it in the former state.
The military operation was launched in January after ULFA members killed 80 people, 60 of them Hindi-speaking migrant workers, in eastern Assam.
Intelligence reports have said that ULFA had shifted its base from Assam to the jungles in adjoining Arunachal Pradesh, while many have sneaked into camps in neighbouring Myanmar after the army offensive.
The ULFA last month rejected Assam government's offer for unconditional talks and warned of stepped up violence, including the use of human bombs to attack selected targets.
Assam Chief Minister Tarun Gogoi had offered unconditional peace talks with ULFA, aimed at ending close to three decades of insurgency in the region.
ULFA said direct talks could be possible only if New Delhi agreed to discuss their core demand of sovereignty or independence, and release five of their jailed leaders.
More than 10,000 people have lost their lives to insurgency in Assam during the past two decades.