Additional troops have been despatched to the north-east

Shivraj Patil said after visiting the state of Assam that the government would take "strong measures" to tackle the violence.

In the latest attack, suspected separatist rebels shot dead six villagers in Assam on Sunday night.

The deadliest attacks, in neighbouring Nagaland, claimed 36 lives on Saturday.

The BBC's Subir Bhaumik in Calcutta says the weekend's bloodshed is the worst for years and shows the rebels have regrouped after offensives against their bases in Bhutan and Burma earlier in the year.

BJP anger

One militant group, the United Liberation Front of Assam (Ulfa), has said it carried out some of the attacks. The authorities suspect a second group, the National Democratic Front of Bodoland (NDFB), is also to blame.

This weekend saw the 18th anniversary of the NDFB's fight for an independent homeland for Bodo people in Assam.

India's violent north-east

Mr Patil said militants were striking "soft targets", adding: "Our first priority is to instil confidence in people and provide security to them."

He said additional troops were being dispatched following a request from Assam's government.

But he also suggested that Delhi was open to negotiations: "Let the militant groups come and talk to us, we are prepared to discuss all issues."

The leading opposition Bharatiya Janata Party attacked the government over its handling of the violence.

Party spokesman, Mukhtar Abbas Naqvi, said: "The United Progressive Alliance government does not seem to be serious about tackling the issues of national security, terrorism and separatism."

Many businesses and schools were closed in some parts of Assam on Monday in response to a strike call from students in protest at the violence.

In the latest attack, police said suspected rebels entered the village of Jhinjhia, about 200km (125 miles) north of Assam's capital, Guwahati, on Sunday night, lined up some of the village men and shot dead six of them.

In the rest of the weekend's attacks:

• Two bombs in Dimapur, Nagaland, on Saturday kill 36

• Ten die in a gun attack and one man is lynched in Makri Jhora on Saturday

• Nine die in other gun and bomb attacks in west Assam on Saturday

• Five people, including two suspected rebels die in explosions in village markets, an electricity grid and at a gas pipeline in Assam on Sunday

• Three die in a blast in Bijni, western Assam, on Sunday

• Three are killed in an explosion at a fish market in Gouripur, western Assam, on Sunday

Anniversary

Assam's government last week offered a ceasefire to the militant groups, asking for a reply by 15 October.

Speaking to the BBC on Sunday, Ulfa commander-in-chief Paresh Barua ruled out talks with the state government.

NATIONAL DEMOCRATIC FRONT OF BODOLAND Separatist group of the Bodo tribe, who accuse authorities of plundering the region's natural resources and flooding it with outsiders. One of around 30 groups fighting for greater autonomy or independence in north-east India Suffered major losses in military operations by Indian and Bhutan forces this year Bloodshed coincides with 18th anniversary of founding

But he said he would talk to the federal government - as long as it was ready to discuss an independent state of Assam.

There are around 30 separatist groups fighting for the causes of various ethnic groups in north-east India.

One Naga separatist group, the National Socialist Council of Nagaland, condemned the blasts, saying they were an attempt to "derail and sabotage our peace talks with the Indian government".

Our correspondent says there is little doubt the NDFB and Ulfa carried out the attacks in Nagaland as well - to underline the extent of their co-ordination and reach.

India's recent change of government and civil unrest in nearby Manipur state may also have provided a distraction for the security forces, allowing the rebels to reorganise, some observers suggest.

"The new government had barely settled down when it had to deal with Manipur," former deputy chief of Indian external intelligence BB Nandi told the BBC.