Indian authorities say four policeman were killed on Friday when a land mine blew apart their vehicle in the insurgence-ridden northeastern state of Assam.
No rebel group has claimed responsibility for the blast, which occurred in the tea-growing region of Dibrugarh.
But police say they believe the land mine was triggered by members of the separatist group known as the United Liberation Front of Asom. The front is one of several militant groups that has been fighting for the state's separation from India since 1979.
Separatists believe New Delhi's policies exploit the region's resources and bring little benefits to local residents.
The rebels have intensified their attacks since a truce and peace talks with the government fell apart in late September.