Two men have been arrested in the northeastern Indian city of Patna over the alleged rape of a 50-year-old woman.
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India rape victim's family speak out
A video of the alleged incident, which occurred next to the holy river Ganges, has also been widely shared on social media.
The men reportedly took turns to assault the victim and film it.
Patna police say the woman was reportedly dragged from the Ganges, where she had been bathing, on Sunday morning.
The Times of India reports the woman can be heard asking the men to consider the "sanctity" of the river, whilst also referring to the river as "mother".
In Hinduism, the river Ganges is considered sacred.
Police said the mobile phone used to film the alleged assault had been seized and would be sent to a forensic laboratory for analysis.
File image of Indian women. Source: AAP
Police said they found out about the alleged incident after seeing the clip online.
In a statement, rural superintendent Anand Kumar said the woman did not report the alleged incident.
"She had completely suppressed the ordeal faced on Sunday and told no-one," superintendent Kumar said.
"The matter surfaced only after the video became viral on Tuesday afternoon."
Does India have a problem?
Statistics from India's National Crime Bureau show there were more than 338,000 cases of crimes against women registered in 2016.
India launched its first national register of sex offenders in September in a bid to stem crimes against women as the country reels from a series of high-profile rape cases.
The database is accessible only to law enforcement agencies and not to the public. It has 440,000 names registered, including those convicted of rape, gang rape, child sex crimes and sexual harassment, according to a home ministry statement.
It also provides their photos, addresses and fingerprints, without compromising "any individual's privacy".
The register comes as a spate of sexual assault cases have rocked the country, which was named the most dangerous in the world for women by experts in a report published by the Thomson Reuters Foundation in June.
In April, India's cabinet also approved the death penalty for rapists of girls below the age of 12.
The changes came after the rapes of an eight-year-old girl and a young woman in two states led to widespread protests.
India's National Crime Bureau revealed of the almost 40,000 rapes reported in India in 2016, 40 per cent of those cases involved children.
