Subir Bhaumik BBC correspondent in Calcutta

A faction of the National Socialist Council of Nagaland said at least 15 Burmese soldiers and three rebels had lost their lives.

The Khaplang faction said its rebels had encircled Burmese assault troops early on Wednesday.

The Burmese army has refused to comment on the incident.

The self-appointed home minister of the Khaplang faction, Khunje Ngaimong, told the BBC of the incident over a satellite telephone.

He said the Burmese troops had approached the group's central headquarters in the Tenu Tekhap Joku valley in India's western Sagaing division.

Mr Ngaimong said the Burmese would find it difficult to break through the group's defences as the rebels were in the jungles attacking smaller assault groups, particularly those bringing supplies.

"This will not be as easy as Bhutan. We have tough fighters who can survive in jungles for months and they will keep harassing the Burmese troops and make their supply lines untenable," he said.

'Positive signal'

Bhutan's army launched an offensive against Indian rebels in its territory last month, saying it had destroyed 30 camps.

Indian forces on the Burmese border have been increased

The Burmese army remained tight-lipped on the latest incident but a spokesman told the BBC the government was against what he described as "breeding elements" that were dangerous to the security of neighbours.

The Indian army said it had little knowledge of the Burmese operation but a senior military intelligence official said additional Indian forces had been deployed on the border to prevent rebels crossing.

"The Burmese are sending out a positive signal," the official said, "that they will not tolerate rebels troubling India.

"Though tackling the rebels will not be as easy as in Bhutan, we can make life difficult for them if the two armies throw a proper encirclement and deny them supplies."

Indian officials suspect the Naga rebels may have been joined by those from the United Liberation Front of Assam (Ulfa) - the group targeted in Bhutan.

Last week India said it might launch joint military operations with Burma, also known as Myanmar, against rebels based there.

Analysts say the Burmese army may not be able to overrun and hold the Naga rebel bases because of the difficult terrain and the extended supply lines which the Naga guerrillas can ambush at will.