NEW DELHI — The demonstrators gathered Friday near the steps leading up to a historic mosque in India's capital. When the leader of the protest triumphantly raised a copy of India's constitution, the crowd burst into a deafening roar.

Protests against a new citizenship law once again swept India on Friday, even as police continued to prohibit public gatherings. Internet access was suspended in at least 11 cities. The demonstrations mark the most significant show of opposition to Indian Prime Minister Narendra Modi since he took office in 2014.

On Friday, several rallies took place in Delhi despite a ban on protests. In Uttar Pradesh, India’s largest state, clashes broke out in various cities between stone-throwing protesters and police. Six protesters were killed across the state, according to P.V. Rama Shastri, a senior state police official.

Opposition to the new citizenship law — which includes religion as a criterion for nationality for the first time — has come from Muslims, young people and left-leaning, liberal-minded Indians. They believe the new law is discriminatory and unconstitutional.

Since winning a resounding reelection victory in May, Modi has moved to implement his party’s agenda of emphasizing Hindu primacy in India. That has alarmed those who want India to remain true to its founding principles of secularism as well as many Muslims, who worry they will be treated as second-class citizens.

The Modi government has faced considerable international criticism — including from members of Congress — over its four-month crackdown in Kashmir, India’s only Muslim-majority state. But so far, the reaction by the U.S. government to the passage of the citizenship act has been muted.

Experts said the current protests were unparalleled in recent Indian history. “This is the first time we have such widespread, nationwide protests that are not against corruption, but essentially protests against discrimination,” said Zoya Hasan, a retired political scientist at Jawaharlal Nehru University in Delhi.

For Muslims, the citizenship law is “the thin edge of the wedge,” said Hasan. “This is the first time that they think they are actually being subordinated.”

The Modi government says the measure is meant to help persecuted religious minorities who entered India illegally from Bangladesh, Pakistan and Afghanistan. It creates a fast-track to citizenship for such migrants, provided they belong to one of six religions — a list that excludes Islam.

Modi’s second-in-command, Amit Shah, has repeatedly stated that the law is a prelude to an even bigger exercise — creating a nationwide registry of citizens where all Indians could be required to prove their nationality. Many Muslims believe such a registry would aim to target their claims to citizenship.

“It is definitely a significant juncture for Indian Muslims; their constitutional rights are being eroded,” said Sitaram Yechury, a senior leader of a major leftist party in India. “But this is not confined to one [religious] community alone.” He said the protests were an “accumulated outburst” against the government born out of frustration that “the secular character of our country is being eroded.”

Although the protests against the citizenship law show no sign of flagging, the government has not given any indication that it will back away from the measure. Modi has not commented publicly on the protests since Tuesday, when he portrayed them as being instigated by the opposition Congress Party.

No public opinion polls have been carried out on the citizenship law, and it is difficult to gauge how much support there is for the measure. But “one gets the sense that Modi, in his second term, is overreaching in some way,” said Neerja Chowdhury, a political commentator in Delhi.

She said the government also had reacted to the protests in a heavy-handed manner — sending police to storm a university and banning public gatherings in Uttar Pradesh — rather than reaching out to protesters.

Faced with continuing unrest, some politicians have distanced themselves from the next part of the government’s agenda. The governing parties in two Indian states — which both voted in favor of the citizenship law in Parliament last week — have since indicated that they will not implement a national register of citizens in their states.

The government should “pause, take corrective measures and retract” in light of public anger, said Pavan Varma, a spokesman for a regional party in the state of Bihar and an ally of the Modi’s ruling Bharatiya Janata Party.

On Friday, several protests were organized in Delhi, and numerous transit stations were again shut to prevent movement of protesters. Police prevented protesters from carrying out marches and barricaded roads to block their movement.

More than 1,000 people gathered near Delhi’s Jama Masjid, a 17th-century red sandstone mosque in the heart of the old city, where they chanted slogans against Modi and waved Indian flags under the watchful eyes of hundreds of police officers.

“It is not a fight only for Muslims,” said Mohammad Hamza, 18, a university student. “It is a fight to save our country. Modi is trying to break us.”

Protesters carried signs against the citizenship law and the proposed nationwide register of citizens. Some in the crowd voiced anxiety at the idea of submitting documents to a potentially byzantine process of verifying citizenship.

Mohammad Imran, 46, said the process would be stacked against Muslims, likening it to a recent landmark Supreme Court verdict that awarded the site of a razed mosque to Hindus. “If we couldn’t protect our mosque in court despite all the documents, how will we prove ourselves as Indians?” he said.

Tania Dutta in New Delhi contributed to this report.