Photo/Illutration Policemen in plain clothes detain a youth during a protest against a new citizenship law in Ahmadabad, India, on Dec. 16. (AP Photo)

NEW DELHI--Students involved in a massive weekend protest at a predominantly Muslim university in India's capital described a clash with baton-wielding police at a news conference Tuesday, while opposition grew nationwide against a new law that provides a path to citizenship for non-Muslim migrants.

A march by students from New Delhi's Jamia Millia Islamia University descended into chaos Sunday when demonstrators set three buses on fire. Police responded with rubber bullets and tear gas. Video footage showed officers running after unarmed protesters and beating them with wooden sticks.

“The 15th of December is a black day in the history of this country," human rights activist Farah Naqvi said at the news conference.

The police response to Sunday's protest has drawn widespread condemnation. It also seems to have sparked an even broader movement against the Citizenship Amendment Act, with demonstrations erupting across the country.

The new law applies to Hindus, Christians and other religious minorities who are in India illegally but can demonstrate religious persecution in Muslim-majority Bangladesh, Pakistan and Afghanistan. It does not apply to Muslims.

Prime Minister Narendra Modi's ruling Hindu nationalist Bharatiya Janata Party has painted the new law as a humanitarian gesture.

“This Act illustrates India’s centuries old culture of acceptance, harmony, compassion and brotherhood," Modi tweeted Monday.

But critics say it is intended to help the party transform a multicultural and secular India into a Hindu “rastra," or distinctly Hindu state and further marginalize India's 200 million Muslims.

India is 80 percent Hindu and 14 percent Muslim, which means it has one of the largest Muslim communities of any country in the world.

“It is as if Indian citizens are rising to save the Indian Constitution from the Indian state and the state policy," said Naqvi, the activist.

Police spokesman M.S. Randhawa said 10 people were arrested during Sunday's protest from Jamia Nagar, a Muslim neighborhood near the university.

“We found out that the arrested men had instigated the crowds and were also responsible for also vandalizing the public property,” Randhawa said.

Students said police lobbed teargas shells inside the campus, broke down the doors of the library and yanked students out to assault them. Dozens of students were taken to local hospitals for treatment.

Police have denied the charges and said they acted with restraint.

The citizenship law follows a contentious citizenship registry process in northeastern India's Assam state intended to weed out people who immigrated to the country illegally.

Nearly 2 million people in Assam were excluded from the list, about half Hindu and half Muslim, and have been asked to prove their citizenship or else be considered foreign. India is constructing a detention center for some of the tens of thousands of people the courts are expected to ultimately determine came to the country illegally.

India's powerful home minister, Amit Shah, has pledged to roll it out the program nationwide, promising to rid India of “infiltrators."

The Citizenship Amendment Act could provide protection and a fast track to naturalization for many of the Hindus left off Assam's citizenship list, while explicitly leaving out Muslims.

The backlash to the law came as an unprecedented crackdown continued in Kashmir, India's only Muslim-majority area, which was stripped of special constitutional protections and its statehood in August. Since then, movement and communications have been restricted.

“Our country is not just for Hindus," said Chanda Yadav, 20-year-old Hindi literature student who was participating in a sit-in Monday at Jamia Millia Islamia University. “I feel it is my moral right to protest against something which divides us as a community.”