CNN  — 

Deadly protests erupted in at least 15 cities in India Thursday, despite strict bans on public gatherings in several areas, as public anger over a controversial new citizenship law considered by many to be discriminatory against Muslims continues to build.

At least three people died in the violence, as thousands took to streets across the country. Two people died from injuries sustained during a protest in the city of Mangalore, in the southern state of Karnataka, a senior doctor at the Highland Hospital told CNN. One more person died from firearm injuries during a protest in Lucknow, the capital of northern Uttar Pradesh state, according to a senior doctor at the King George Medical University in the city.

In Uttar Pradesh, protesters and police violently clashed in Lucknow, with buildings and vehicles set alight. And in Sambhal city buses were torched by protesters.

In the capital New Delhi attempts by authorities to prevent demonstrations proved ineffective, as large crowds brought parts of the downtown area to a standstill.

Several metro stations were closed, with Delhi Metro Rail Corporation citing “sudden safety and security reasons.” Heavy traffic also prompted airlines Air India and Indigo to offer a full refund for all outbound domestic and international flights from the capital.

Large crowds also gathered in major cities including Mumbai, Kolkata, Hyderabad, Malegaon, and Chennai. By midday, police had detained 70 people in the southern city of Bengaluru after protesters refused to disperse from two locations.

Fueling the protests is nation-wide anger over the Citizenship Amendment Act (CAA), which was signed into law last week. The law promises to fast-track Indian citizenship for religious minorities from three neighboring countries who arrived before 2015 – but not if they are Muslim.

Critics say the law is unconstitutional as it bases citizenship on a person’s religion and would further marginalize India’s 200-million strong Muslim community.

Colonial-era law

The Indian government had sought to quell any unrest over the law’s passing. Last week, authorities shut down the internet in four northeastern states after violent protests broke out. And on Thursday, a colonial-era law that prevents gatherings of four or more people – known as Section 144 – was imposed in three areas.

New Delhi police imposed Section 144 around the Red Fort ahead of Thursday’s protest, after police denied permission for the march. The law was also imposed in Bengaluru, and across the entire state of Uttar Pradesh – India’s largest and most populous.

Organizers of nationwide action called for people to gather regardless of the prohibitory restrictions. “Section 144 being imposed by the police is an attempt to thwart our march. This will not deter us. We will gather there for our march,” Yogendra Yadav, founder of Swaraj Abhiyaan, a group that organized the march told CNN ahead of Thursday’s march in Delhi.

Many of who marched said the government is using bans on public gatherings to muzzle the voices of Indian people.

“This was to be a peaceful protest by citizens who wish to uphold the values of our Constitution. You have used a colonial-era law to suppress us and our voices,” India historian Ramachandra Guha wrote on his official Twitter account on Thursday.

In New Delhi, telecoms company Vodafone India tweeted that its services had been suspended in several parts of the city, “as per the directive received from the government.” It comes amid reports in multiple local media outlets that the government ordered the suspension of mobile and data services in parts of the capital as protests got underway.

Vodafone tweeted in a reply to a customer that services were stopped in six locations across the city. CNN has reached out to local authorities for confirmation.

Outside of Delhi’s Red Fort, demonstrators said it was their right to protest.

“What they’re doing is wrong. We oppose the CAA. We oppose not being allowed to protest. We are Indian and Muslim. We can be both. All religions can live in India,” said local resident Rubina Zafar.

Protests escalate

The restrictions come after ongoing protests against the citizenship law have turned violent in recent days, with police and protesters involved in street clashes.

Hundreds of people were injured and dozens arrested on Sunday after police stormed a university campus in New Delhi, firing tear gas. And on Tuesday further violent clashes between protesters and police broke out in the district of North East Delhi.

In the northeastern state of Assam ongoing protests have turned deadly, with at least five people killed, police said.

Protests in the northeast are different, however. Many indigenous groups there fear that giving citizenship to large numbers of immigrants would change the unique ethnic make-up of the region and their way of life, regardless of religion.

The widespread civil action comes a day after India’s Supreme Court refused to halt implementation of the citizenship law, though it will hear a raft of petitions that question the law’s constitutionality.

“It hurts the spirit of India. We are going to fight this till the end,” said Abhishek Manu Sanghvi, a senior leader from India’s main opposition Congress Party on Wednesday.

CNN’s Vedika Sud, Swati Gupta and Manveena Suri contributed reporting.