Burmese troops have begun an offensive to flush out Indian rebel bases in their territory, the Indian army says.

Burma's military ruler, Than Shwe, vowed to help fight the separatists when he visited Delhi last month.

A spokesman for a key rebel group, Ulfa, said it had beaten back the first wave of Burmese infantry.

The attacks coincide with a month-long drive by about 6,000 Indian troops against rebels in India's north-eastern state of Manipur.

Manipur is one of seven north-eastern Indian states hit by separatist violence.

Informed

Burmese troops have attacked bases in its western frontier region of Sagaing and the southern part of Kachin state.

We have repeatedly beaten back the Burmese army from these areas and we will do it again   K Mulatonu, rebel group spokesman

The BBC's Subir Bhaumik in Calcutta says Burma had informed Indian military officials at the weekend about its offensive.

Rebels of the National Socialist Council of Nagaland (Khaplang faction) and the United Liberation Front of Assam (Ulfa) confirmed the attacks.

"They attacked our bases but they were beaten back with casualties and I don't think they will succeed," said Ulfa's military wing chief, Paresh Barua.

He said rebels had mined huge stretches of hill terrain on both sides of the border.

Indian army officials said the Burmese were "holding the border" in the areas opposite Manipur.

K Mulatonu of the NSCN Khaplang faction said Burma was massing more troops and supplies in Sagaing and south Kachin.

"We might expect more attacks from them, but we are prepared. We have repeatedly beaten back the Burmese army from these areas and we will do it again," he said.

Indian Defence Minister Pranab Mukherjee said he hoped Indian rebel bases in Burma would be demolished this year.

The Indian army claims to have overrun more than 30 rebel camps during its four-week operation in Sajit Tampak and the neighbouring Churchandpur regions of Manipur.

The rebels say they have only withdrawn from some of their smaller bases.

"We continue to hold on to our major base area in both Sajit Tampak and Churchandpur," said Tombi Singh, spokesman for another rebel group, the United National Liberation Front.

Both sides claim to have inflicted heavy casualties.

India's north-east is home to more than 200 ethnic and tribal communities and more than 20 rebel groups fighting for greater degrees of independence or tribal rights.