Hundreds of survivors of a brutal rebel attack that killed at least 63 people in northeastern India sought shelter Wednesday in a church and school while security forces imposed a curfew in a bid to contain the latest bout of ethnic violence.

Long-simmering land and ethnic disputes in Assam state erupted in bloodshed Tuesday when authorities said rebels belonging to a faction of an indigenous separatist group called the National Democratic Front of Bodoland attacked tribal settlers known as Adivasi, whose ancestors migrated to Assam more than 100 years ago. Most of them worked on tea plantations.

At least 100 people, mostly women and children, sought refuge in a church in Shamukjuli village in Sonitpur district, where 26 of the victims died. Another 200 people ran to a nearby school. The Adivasis are a mix of Hindus and Christians and many had been preparing for Christmas when the attack took place, survivors said.

Bodo rebels have been fighting for a separate homeland for their indigenous tribe, which makes up 10 percent of Assam's 33 million people. They have staged attacks against both Adivasi and Muslim settlers in violence that has left at 10,000 people dead, most of them civilians, in the last three decades.

Many of the dead in Tuesday's attacks included women and children, police said. The rebels may have been provoked by heavy losses they suffered recently as police intensified operations against the group, Singh said.

"We are trying to ensure that ethnic violence does not flare up," he said, adding that a curfew was imposed in two districts and scores of police and paramilitary forces patrolled the area.

There were concerns the violence could spill over.

Following the attacks, angry Adivasis surrounded a police station in Sonitpur and attempted to attack the officers inside, said S.N. Singh, a top police official. Police opened fire, killing three Adivasis, he said.

He also said there were incidents of Bodo homes being attacked, but troops managed to control the situation.

India's Prime Minister Narendra Modi condemned the latest attacks, and the Home Ministry rushed several thousand federal paramilitary troops to the region, junior Home Minister Kiren Rijiju said.

Dozens of rebel groups have been fighting the government and sometimes each other for years in seven states in northeast India. They demand greater regional autonomy or independent homelands for the indigenous groups they represent.

The rebels accuse the federal government of exploiting the region's rich mineral resources but neglecting the local people.

In May, rebels from the same group shot and killed more than 30 Muslim settlers in the region.