By Matthew Grant
BBC News, Calcutta
The Indian army says it is conducting a major operation against rebel bases in the north-east of the country.
Indian troops are said to be moving in on rebel bases
Burma has sealed its border to prevent militants crossing into its territory from the Indian state of Manipur, where the offensive is focused.
The north-east of India is home to many groups who often cross back and forth into neighbouring countries.
The army began its offensive last month, but waited until now to reveal what is going on in the remote state.
A spokesman for the army said it had surrounded 1,500 fighters belonging to three different rebel groups.
He said Burma had stationed troops along its side of the border to prevent the rebels from escaping.
But the spokesman stressed the action was being taken by the Indian army on its own, with the Burmese simply guarding their frontier.
During a visit to Delhi last week, Burma's military leader promised not to allow insurgents battling India to operate from inside his country.
About 40 different rebel groups exist in the north-east of India, with many believed to use bases in neighbouring countries.
So far, the action in Manipur has led to the deaths of two Indian soldiers and 13 rebels.
The spokesman said the army had also captured 34 insurgents.
He said the rebels were now choked off and soon the army would zero in on their bases.