(Reuters) - India deployed military helicopters to hunt down tribal militants in Assam on Thursday after rebels killed 75 people this week, the deadliest in the remote area in years.

Assam has a history of sectarian bloodshed and armed groups fighting for secession from India.

On Tuesday, suspected militants of a faction of the National Democratic Front of Bodoland attacked four villages in the space of an hour, pulling people out of their homes and shooting them dead.

More than half of the victims were women and children of tea plantation workers from outside the state, Assam Chief Minister Tarun Gogoi said as more bodies were discovered in the remote area.

The attacks appeared to have been in retaliation for an offensive that security forces launched against the Bodo faction a month ago that inflicted heavy losses. The militant group lost 40 men and a huge quantity of arms and ammunition, state police said.

The rebels turned on plantation workers, believing that some were informing the police about their movements.

"This is an act of terrorism. We are going to be very tough," Home Minister Rajnath Singh, who flew to the state, told reporters.

Prime Minister Narendra Modi's government took power in May promising economic development and a tough stance on national security. "We have said there will be zero tolerance for terrorism," Singh said.

India's northeast region, bounded by China, Myanmar, Bhutan and Bangladesh, is home to more than 200 ethnic groups. The region has trailed the rest of India in economic development and the gap has widened in recent years, fuelling discontent.

For decades, the Bodos have been fighting for a state of their own called Bodoland, accusing New Delhi of plundering their state's resources and flooding the area with outsiders. The group follows a distinctive culture and speaks a Tibeto-Burman language.

A military official said helicopters were scouring the jungles of Assam to track down militants trying to flee to Bhutan and the neighboring Indian state of Arunachal Pradesh, which has thickly forested mountains.

About 5,000 additional soldiers have been deployed to Assam in response to this week's attacks, the government said.