PATNA, India - A teenage Indian boy was thrashed, paraded through the streets with his head shaved and then thrown under a train for daring to write a love letter to a girl from a different caste, police said Thursday.

Manish Kumar, 15, was kidnapped by members of the rival caste on his way to school and was killed as his mother begged for mercy, police in the impoverished eastern state of Bihar said.

One man has been arrested and a policeman suspended.

The victim's mother, Lalit Devi, told police she had watched "helplessly" as the wheels of the train passed over her son.

"The accused persons killed the boy for writing a love letter to the girl of the same village," superintendent of police in Kaimur district, Rajesh Kumar, told Reuters by telephone.

Police said the girl belonged to a washerman community, considered a lower caste, whereas the boy came from the slightly higher dairymen Yadav community.

Love across caste lines is often violently opposed, especially in rural northern India, and it is not uncommon for outraged families to kill to "save the family honor."