Prime Minister Manmohan Singh has promised to protect India's Christians in a letter to the widow of an Australian missionary killed nine years ago in a sectarian attack in the east of the country.
Graham Staines and his two young sons were burnt alive in January 1999 as they slept in their jeep in Orissa state by a right-wing Hindu mob that accused them of trying to convert the local population.
"The government will take all necessary steps to safeguard the fundamental rights and liberties of all sections of our society and protect their religious freedom," Singh wrote to Gladys Staines, a statement from his office said.
"We will not tolerate any efforts aimed at disturbing the communal harmony or secular fabric of our country."
Gladys Staines had expressed concerns about increasing sectarian tension in Orissa in a letter to Singh dated December 20, the statement said.
A few days later, nearly a dozen churches were damaged and a man killed on Christmas night during a protest backed by a right-wing Hindu group. Subsequent clashes between Hindus and Christians left four deader.
Nearly 500 Hindus and Christians have since moved to relief centres for safety.
Hardline Hindus accuse Christian missionaries of aggressively converting low-caste Hindus -- who face discrimination from higher castes -- by force or by offering incentives such as free education.
Orissa state laws on religious freedom require every change of religion to be cleared by the authorities. Hindus say the missionaries fail to do so.
The rights group Human Rights Watch has called for an independent inquiry to identify those instigating the violence in Orissa.
The rising tensions have prompted several Indian state governments to enact anti-conversion laws.
Sectarian clashes erupt periodically in India, where only 2.3 percent of the billion-plus populations are practising Christians.
A Hindu man is serving a life sentence for the deaths of Staines and his two sons as well as another Catholic priest in Orissa.
Gladys Staines moved back to Australia three years ago but continues to visit the state where her husband spent decades working with leprosy patients.