NEW DELHI — After spending several anxious days in prison, Natasha Narwal, a student activist accused of rioting by the New Delhi police, thought her ordeal was nearing an end.

A judge ruled that Ms. Narwal had been exercising her democratic rights when she participated in protests earlier this year against a divisive citizenship law that incited unrest across India.

But shortly after the judge approved Ms. Narwal’s release in late May, the police announced fresh charges: murder, terrorism and organizing protests that instigated deadly religious violence in India’s capital. Ms. Narwal, 32, who has said that she is innocent, was returned to her cell.

“I felt like crying,” said her roommate, Vikramaditya Sahai. “We are grieving the country we grew up in.”

As India struggles to quell surging coronavirus infections, lawyers accuse the authorities of seizing on the pandemic as an opportunity to round up critics of the government who are protesting what they see as iron-fisted and anti-minority policies under Prime Minister Narendra Modi.

In recent weeks, Ms. Narwal and nearly a dozen other prominent activists — along with potentially dozens of other demonstrators, though police records are unclear — have been detained. They are being held under stringent sedition and antiterrorism laws that have been used to criminalize everything from leading rallies to posting political messages on social media.

India’s coronavirus restrictions, some of which are still in effect, have blocked pathways to justice, lawyers and rights activists say. With courts closed for weeks, lawyers have struggled to file bail applications, and meeting privately with prisoners has been nearly impossible.

Law enforcement officials in New Delhi, who are under the direct control of India’s home ministry, have denied any impropriety. But rights groups say the arrests have been arbitrary, based on scant evidence and in line with a broader deterioration of free speech in India.

In a lengthy report released this month, the Delhi Minorities Commission, a government body, accused the police and politicians from Mr. Modi’s party of inciting brutal attacks on protesters and supporting a “pogrom” against minority Muslims.

Meenakshi Ganguly, the South Asia director of Human Rights Watch, said cases against the activists appeared to be “politically motivated,” and that the police have devised a formula for keeping people like Ms. Narwal in jail: When a judge orders the release of a prisoner for lack of evidence, new charges are introduced.

“The urgency to arrest rights activists and an obvious reluctance to act against violent actions of the government’s supporters show a complete breakdown in the rule of law,” she said.

Before the pandemic hit, Mr. Modi was in the throes of the most significant challenge to his power since becoming prime minister in 2014. After Parliament passed a law last year that made it easier for non-Muslim migrants to become Indian citizens, millions protested across the country.

To critics, the citizenship law was more evidence that Mr. Modi’s Hindu nationalist government planned to strip the country’s Muslims of their rights.

Tensions peaked in February when sectarian violence and rioting broke out in New Delhi. The vast majority of people killed, hurt or displaced were Muslim, and the police were involved in many of those cases.

After Mr. Modi announced a nationwide lockdown in late March to contain the coronavirus, shutting down businesses and ordering all 1.3 billion Indians inside, the protests disbanded. Lawyers said the police then moved to detain demonstrators while skirting complaints against government allies.

Among those in custody are a youth activist who raised awareness about police brutality against Muslims; an academic who gave a speech opposing the citizenship law; and Ms. Narwal, a graduate student who co-founded Pinjra Tod, or Break the Cage, a women’s collective that organized some of the largest rallies.

Nitika Khaitan, a criminal lawyer, said the crackdown has also pushed beyond higher-profile critics to include ordinary residents living in riot-hit neighborhoods. She recently challenged those arrests in a jointly signed letter to the Delhi High Court.

Lawyers have tracked a few dozen such arrests under the lockdown, though Ms. Khaitan said the true figure could not be verified because police reports have not been made public. Many detentions were “not in compliance with constitutional mandates,” she said.

In a recent interview, Sachidanand Shrivastava, the police chief in New Delhi, said his officers were conducting fair investigations.

In May, the authorities said they had detained about 1,300 people for involvement in the protests and riots, including an equal number of Hindus and Muslims. Recently, the police arrested a group of Hindus for forcing nine Muslim men to chant “Hail Lord Ram,” a reference to a Hindu god, before killing them and throwing their bodies into a drain.

“It is very important that the police force remain impartial,” Mr. Shrivastava said. “And we are following this principle from Day 1.”

But members of India’s judiciary have questioned the official numbers, accusing the police of withholding information about the arrests under national security protections and singling out Muslims for many of the harsher charges.

In court proceeding notes reviewed by The Times, a judge hearing a case against a Muslim protester wrote that the police appeared to only be targeting “one end” without probing the “rival faction.” During the riots, the police were accused of abetting Hindus and, in some cases, torturing Muslims.

Khalid Saifi, a member of United Against Hate, a group that works with victims of hate crimes, was arrested after he tried to mediate between the police and protesters, according to his lawyers.

The police charged him with being a “key conspirator” of the riots. His wife, Nargis Saifi, said he was tortured in custody.

“His only crime is he is a Muslim,” she said.

M.S. Randhawa, a police spokesman, denied that Mr. Saifi had been tortured, adding that he has regular opportunities to speak to a judge if abuse occurs.

“These are just allegations,” Mr. Randhawa said. “He would have told the magistrate if he had been tortured.”

But rights advocates accuse Mr. Modi’s government of shielding party officials — and more broadly, of Hindus involved in the violence.

Ms. Narwal, who was detained in May, could face at least several years in prison for helping organize demonstrations that blocked a busy road in northeast Delhi, where February’s bloodiest battles between Hindus and Muslims broke out.

The police have accused her of playing a leading role in the riots, charging her with murder, attempt to murder and being part of a “criminal conspiracy.”

At the same time, the police have been accused of ignoring complaints against Kapil Mishra, a local politician with Mr. Modi’s Bharatiya Janata Party who gave a fiery speech threatening to forcibly remove Ms. Narwal and other protesters if the authorities did not take action.

Hours after the ultimatum, the streets erupted. But charges were never filed against Mr. Mishra, who has denied a role in starting the riots.

A New Delhi police superintendent, who spoke on the condition of anonymity, said some officers had wanted to act against Mr. Mishra, but they were pressured by the force’s leadership not to touch “the warriors of the government.”

“We did not even try,” the superintendent said. “The directions were clear: Don’t lay your hands on him.”

Through an intermediary, Mr. Mishra declined to comment.

Ms. Narwal’s father, Mahavir Narwal, said the government was moving India closer to authoritarianism and demonizing anybody who questioned their policies.

For weeks, prison officials ignored his calls and emails to Tihar Jail, where Ms. Narwal is being held. With coronavirus restrictions in place, she was moved into an isolation ward at one point, where she stayed for 17 days, said Mr. Narwal, a retired scientist.

Lately, communication has smoothed out. But Mr. Narwal said the subtext of his daughter’s arrest seemed clear: “If you protest, you will be called a terrorist.”

“All she did was fight to keep the soul of India alive,” he said.

Karan Deep Singh contributed reporting.