On a recent afternoon, pastor Anthony Francis surveyed the blackened interiors of the St Sebastian Catholic church in northeast Delhi, his boots scrunching among the rubble and glass shards littering the floor. A fire on December 1 gutted much of the building, including the prayer hall, altar, bibles and statues. The 48-year-old priest pointed to the truncated ceiling fans whose blades melted in the inferno. The flames also reached the upper floor, licking rows of pews, stripping them down to their metal frames.

"This was no accident. We believe this was a deliberate act of arson. There was certainly foul play involved," the pastor said, adding that the church smelt strongly of kerosene afterwards and church members spoke of seeing oil in the water after the fire was put out.

Since the incident, at least five Catholic churches in and around Delhi have reported attacks, including burglary, suspected arson, vandalism and stone-throwing, raising concerns about a deliberate campaign of violence.

The St Sebastian church in northeast Delhi shares a wall with a Hindu temple

Fears about religious freedom in India have heightened since Prime Minister Narendra Modi and his Hindu nationalist Bharatiya Janata Party (BJP) swept to power last May. And, church leaders say the authorities are not taking the attacks seriously.

"The government, including the prime minister, has still said nothing to condemn the attack," Francis said, adding that the fire had rattled his congregation of about 300 families. "This took place right in the heart of the capital. How can any religious minority anywhere in India feel safe anymore?"

Conversion controversy

It is a question that threatens to tarnish Modi's reform drive and his high-octane efforts to raise India's profile. Critics say that the BJP's rise to power has emboldened hardline grassroots groups affiliated to the party who want to make India a nation of Hindus. In recent months, reports of mass "reconversion" ceremonies for Christians and Muslims have caused controversy and sparked an uproar in the country.

Analysts say Modi, who has a controversial past himself, has failed to take an unequivocal stance on reconversion, an issue that threatens to undermine the secular foundations of multi-faith India which counts around 180 million Muslims or around 14 percent of its 1.3 billion population. The Christian minority is significantly smaller, accounting for just over two percent of the population.

"Modi's silence can be interpreted as acquiescence. If his public agenda and his promise to the country to bring inclusive development have to carry conviction then he has to stand up and be counted against such groups with divisive tendencies," Vinod Sharma, political editor of daily Hindustan Times, said.

'Back to the roots'

The groups in question belong to the same broad ideological family as the BJP. Chief among them is the Rashtriya Swayamsevak Sangh (RSS), a Hindu supremacist organization founded in 1925, and often referred to as the "ideological fountainhead" of the BJP. Modi himself was a full-time RSS worker at one time.

Another affiliated group, the Vishva Hindu Parishad (VHP), is reported to have been behind recent "reconversions" of Christians in West Bengal and the southern state of Kerala. But VHP spokesman Surendra Jain insisted they were doing nothing wrong and were not using any force. Conversion in India is illegal if there is any element of compulsion or bribery.

"We are not doing conversions, we are conducting homecoming ceremonies to bring people back to their original religion," Jain said. "It's a back to the roots campaign. After all, everyone knows that their ancestors were Hindu."

'Using the ghost of the past'

Going back in history is the best way to understand the current controversy, according to Nilanjan Mukhopadhyay, Delhi-based political journalist and author of the 2013 biography, "Narendra Modi: The Man, the Times." He pointed out that religious conversions have always been a hot button issue for Hindu nationalists in India, which was colonized for centuries by Muslim and Christian invaders.

The fire destroyed many of the church's holy books

In the early 1950s, the RSS began a campaign to bring the largely impoverished tribal community – long the target of Christian missionaries in the 18th and 19th centuries – back into the Hindu fold. And, those efforts have continued over the decades with varying degrees of intensity, and violence, Mukhopadhyay said, depending on the political influence of Hindu nationalists in New Delhi.

"There is little doubt that Christian missionaries during the colonial era used inducements to lure people to convert," the expert on Hindu rightwing politics said. "But there is no data to suggest India's Christian population has been growing in the decades since it won independence in 1947. But Hindu groups are still using the ghost of the past to create a monster."

That is hardly likely to reassure members of Delhi's Christian minority. Philomina Alosious, a member of the burned St Sebastian church, said she remained "shocked and scared" since the fire. "Our neighbors and friends have advised my children to go away from India and look for jobs abroad," the 61-year-old said. "I think that is the only way they will be safe."