NEW DELHI — The remote, destitute state of Orissa, marred for years by Hindu-versus-Christian violence, erupted in a retaliatory killing on Monday after the murder of a Hindu leader led a mob to burn small Christian churches, prayer halls and an orphanage that had housed 21 children.

The police said a woman’s body, charred beyond recognition, was found inside the church orphanage. The church’s pastor, whom the police did not identify and who was injured in the fire, told the authorities that the body was that of a nun working there. No children were injured.

The attack on the orphanage on Monday, in an isolated district called Bargarh, came after the killing Saturday of a Hindu leader who had been associated with the Vishwa Hindu Parishad, or World Hindu Council, and who was leading a drive to wean local villagers from Christianity. Radical Hindu groups like the council are vehemently opposed to conversions to Christianity, which in India tend to focus on traditionally downtrodden lower-caste and indigenous groups, and have lately taken to conducting mass ceremonies to convert them back to Hinduism.

The Hindu leader who was killed, Laxmanananda Saraswati, was among five people slain by unidentified armed men who stormed a Hindu school in the nearby district of Kandhamal. The police blamed Maoist insurgents who prevail in the area. Mr. Saraswati’s followers, however, blamed Christians, and called for a statewide strike on Monday. The state government ordered all schools closed.