PATNA, India (AFP) - A low-caste teenage boy was burnt to death in eastern India for letting his goat stray into paddy fields belonging to a high-caste farmer, police said Thursday.

Police arrested the farmer thought responsible for the attack on the 15-year-old boy, whose Mahadalit caste is the lowest in India's still deeply entrenched hereditary social system.

The boy, Sai Ram, was attacked on Wednesday night in a village in Rohtas district of Bihar, one of India's most populous, underdeveloped and impoverished states.

"Ram was first badly beaten by (the) accused and later set on fire. He was declared dead when brought to a local government hospital," said Chandan Kushwaha, superintendent of police in Rohtas.

Kushwaha said police had registered a murder case against the farmer, who was arrested on Thursday, after the boy's family went to police requesting action.

"Police have begun their investigation into the case and raids continued to arrest the accused, who had absconded after the incident," he told AFP.

More than 138 million Indians belong to the lowest caste known as the Dalits, or "the oppressed," the term the community prefers to the archaic "untouchables".

In Bihar, the Mahadalits have been classed by the state government as the poorest of the Dalits.

Angry members of the opposition Communist Party of India protested in the area against the attack, blocking roads, the Press Trust of India (PTI) news agency reported.

State chief minister Jitan Ram Manjhi, himself a Mahadalit, demanded swift action to bring those responsible to justice, and pledged compensation for the boy's family, PTI reported.