Authorities have imposed an emergency law banning large gatherings in parts of India’s capital, Delhi, as nationwide protests escalated, injuring police and demonstrators.

A week after a controversial new citizenship law was passed by parliament, which has been accused of openly discriminating against Muslims, protests across the country showed no sign of abating.

Clashes between demonstrators and police in the Seelampur district of Delhi turned violent on Tuesday, with 21 injured and buses and a police outpost set alight, leading police to bring in emergency measures to prevent the gathering of more than four people in certain Muslim-dominated areas of the city.

Under the new legislation, tens of thousands of Hindu, Christian, Jain, Buddhist and Sikh migrants from Bangladesh, Pakistan and Afghanistan will be allowed to claim Indian citizenship. The same will not apply for Muslims, who the BJP government argues are not a threatened minority in these countries.

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Some of the most violent altercations between protesters and police over the past week have occurred on Muslim-majority university campuses, where students who were marching against the citizenship law were met with police brutality.

Harsh Mander, a prominent human rights activist, said he would be filing an official complaint of serious police atrocities over officers’ actions at Aligarh Muslim University (AMU) in Uttar Pradesh on Sunday. Police violently stormed the campus, firing teargas and detaining dozens of Muslim students.

Facebook Twitter Pinterest A protest against the Citizenship Amendment Act in Mumbai, India, on Wednesday. Photograph: Rajanish Kakade/AP

Speaking to the Guardian, Mander said multiple students and teachers recounted how the police had used Islamophobic slurs and taunts at the Muslim students as they beat them with batons, including calling them “khatana”, which means circumcised, and shouting the Hindu nationalist slogan “Jai Shri Ram”, meaning Hail Lord Ram, a Hindu God.

He also spoke on behalf of another 19-year-old AMU student, who did not want to speak to the media directly for fear of retribution, who had been detained and beaten by police for almost 24 hours.

“When they brought him to the police station, he described the hateful Islamophobic taunts that the police were saying to him,” said Mander. “They beat him up so badly that his hand was broken, and even after they broke it, they kept beating him. He showed me the terrible marks all over his body.”

Mander alleged that those students who had been attacked by the police had been informed by the university administration that if they filed an official complaint they would be both expelled and also be charged under the national security act.

“The openness of the Islamophobia of the police here is what really troubles me,” said Mander. “We’ve transitioned from vigilante lynching, where the government created an enabling environment for hate, into the state actually doing it itself. What this citizenship act and the police response to the protests makes clear is this government has declared war on its Muslim citizens.”

Facebook Twitter Pinterest Women protest outside Jamia Millia Islamia University over India’s new citizenship law. Photograph: Money Sharma/AFP via Getty Images

While the BJP government has widely denied that the citizenship act discriminates against Muslims, critics say it is their most explicit attempt yet to forward their Hindu nationalist agenda and divide the country down religious lines.

It followed reports of “barbaric” violence against students at the Muslim-majority Jamia Millia Islamia University in Delhi on Sunday, where dozens were injured, including one student who lost an eye after being hit with a teargas canister.

On Tuesday night, the UN raised concerns about the “excessive force” used against students. Stéphane Dujarric, a spokesperson for the UN secretary general, said: “We call for restraint and urge full respect for the rights of freedom of opinion and expression and peaceful assembly.”

In Assam, the north-eastern state where the protests first began a week ago, and where six people have lost their lives in the clashes so far, thousands of government employees took to the streets.

Among the demonstrators was eminent Assamese literary critic and social scientist Hiren Gohain, who described the new citizenship law as “ghastly and malicious”.

“We want to maintain our the tradition of social harmony,” said Gohain. “We are at one with the rest of the country in opposing an unconstitutional, communal idea of citizenship. If people want freedom, if they don’t want to be slaves, they will have to maintain the struggle.”

Meanwhile, the Urdu writer Mujtaba Hussain declared he would return his Padma Shri award in protest against the Citizenship Amendment Act. “The situation in the country is becoming worse day by day and in my lifetime I have never witnessed such situations … the country is getting separated in the name of religion and hatred,” he said.

Ahmer Khan contributed reporting from Assam