Violent attacks on religious minorities in India averaged one attack per day last year, a rising number that has led a coalition of US Congress members to plead with India's leaders to condemn the violence.

According to the Catholic Secular Forum, attacks rose more than 20 percent from 2014 to 2015. There have been 36 attacks on Christians so far this year, ranging from churches being destroyed to priests, nuns, and parishioners being beaten, according to the Christian human rights group International Christian Concern (ICC), as well as four murders of Muslim men by Hindu mobs over their consumption of beef.

Christian rights groups monitoring the violence say the attacks have coincided with a strong rise in Hindu nationalism, which encompasses a broad spectrum of Indian political movements, but centers around the idea that Hindu traditions and beliefs should serve as a guide for the state and its citizens. The more extreme Hindu nationalists are accused of mounting the attacks.

The extremists have been ignored, if not outright condoned, by the country's prime minister, Narendra Modi, and ruling party, the Indian People's Party, which both came to power amid the rising nationalist tide.

"It's a radical Hindu ideology," said William Stark, an expert in South Asia with ICC. "If you see someone Muslim or Christian, they're following a foreign faith, and they're defiling India because they're following a foreign faith."

Meenakshi Ganguly, South Asia Director of Human Rights Watch, said the attacks were being carried out by "vigilante groups" who claim to be supporters of the ruling party. They have taken up various courses of action, including trying to ban the consumption of beef nationally and trying to convert Christians to Hinduism, he said.

"Religious minorities, particularly Christians and Muslims, are feeling increasingly vulnerable," Ganguly said.

About 80 percent of India's population of 1.3 billion people are Hindu, Stark said, followed by about 12 percent Muslim, two to three percent Christian, and under two percent Sikh. There are about 25 million Christians in the country currently, but there's been an increase in conversion among those of the lowest social class, once known in Indian culture as the "untouchable" caste, for whom Christianity is appealing, he said.

"You're in a religion that for thousands of years said you're something below human, and then a faith comes that says everybody is created equal, that's a very attractive message," he said.

In addition to violent attacks, some towns and regions have passed discriminatory laws barring Christians, Muslims, and Sikhs from living inside village borders, accessing public utilities like water wells, or farming nearby lands, Stark said. He called the laws "social boycotts."

34 members of the US Congress, including eight senators and 26 representatives from both parties sent a letter to Modi in February expressing their "grave concerns about the increasing intolerance and violence members of India's religious minority communities experience."

"We urge your government to take immediate steps to ensure that the fundamental rights of religious minorities are protected and that the perpetrators of violence are held to account," they wrote.

Stark described an incident earlier this month in which a Pentecostal church was overrun by a mob during church services. Some of the 60 Christians praying inside were beaten, while the church, its Bibles, and furniture were broken and vandalized.

The persecution is "very much a regional issue," David Curry, CEO of the Christian group Open Doors, which monitors persecution of Christians around the world, pointed out. It is mainly concentrated in the southern region of India.

"You've got, just like in other religions, an extremist group that believes their religion should be an enforced national faith, and there are those forces within India, yet there are also people who want to have freedom of religious expression," he said.

"It could be that some of these extremists feel emboldened because they feel perhaps that they have somebody who won't pursue them," Curry said of Modi's government. "We haven't seen Mr. Modi step out and protect these Christians and we think he should. It's a very dangerous thing if he continues to let these kinds of attacks go unanswered. "

The government has remained "eerily silent," Stark said, leaving religious minority members feeling vulnerable. The foreign minister responded to Congress's letter by calling the attacks "an aberration," and a recent scheduled visit by the International Commission for Religious Freedom was canceled when India suddenly denied the group its visas, Stark said. The government's lack of action amounts to tacit approval and sends a signal of impunity toward those perpetrating the attacks, he said.

"In the West we have this perception of Hinduism as yoga and meditation, a very peaceful eastern religious ideology. And there are millions like that but there are also radical elements," Stark said.