Sporadic violence hit parts of Delhi overnight as gangs roamed streets littered with the debris of days of communal riots that have killed 35 people so far, police said Thursday.

Thousands of riot police and paramilitaries patrolled the affected northeast fringes of the Indian capital of 20 million people, preventing any major eruptions.

The unrest is the latest bout of violence over Prime Minister Narendra Modi's citizenship law, which triggered months of demonstrations that turned deadly in December.

Sunil Kumar, director of the Guru Teg Bahadur (GTB) Hospital, said Thursday the hospital registered 30 deaths while the chief doctor at Lok Nayak Hospital said that two people had died there.

"All of them (at the GTB) had gunshot injuries," Kumar told AFP.

The new fatalities -- up from 27 on Wednesday -- were all from the violence on Monday and Tuesday when mobs of Hindus and Muslims fought running battles. 

Homes, shops, two mosques, two schools, a tyre market and a fuel station were torched. More than 200 people were also injured.

"No major incident of violence was reported from anywhere in the affected areas" overnight Wednesday to Thursday, Mandeep Randhawa, Delhi police spokesperson, told AFP. "Some distress calls were made and the force provided immediate assistance," he said.

The initial violence erupted late Sunday after Hindu groups objected to Muslims holding a street demonstration over the citizenship law.

Mobs armed with swords and guns set fire to thousands of properties and vehicles. Locals complained that police did nothing to stop the violence. 

In December at least 30 people were killed, mostly in police action in northern Uttar Pradesh state, a part of the country with a significant Muslim population.

Many Muslims believe the citizenship law in combination of a mooted citizens' register will leave them stateless and is part of a plan by Modi's right-wing ruling party to turn officially secular India into a Hindu nation. 

His party has denied the allegations but in recent weeks members have called protesters "anti-nationals" and "jihadists", with some calling for them to be jailed or even shot dead.

Meanwhile, a US government commission on Wednesday faulted India's response to deadly communal riots in New Delhi and urged the government to take swift action to protect the Muslim minority.

The US Commission on International Religious Freedom, which advises the US government but does not set policy, voiced "grave concern" about the violence which broke out as President Donald Trump was visiting.

"One of the essential duties of any responsible government is to provide protection and physical security for its citizens, regardless of faith," said chairman Tony Perkins, a conservative Christian close to the Trump administration. 

"We urge the Indian government to take serious efforts to protect Muslims and others targeted by mob violence," he said in a statement.

Anurima Bhargava, a commissioner appointed by Democratic House Speaker Nancy Pelosi, voiced alarm at reports that Delhi police "have not intervened in violent attacks against Muslims."

"The brutal and unchecked violence growing across Delhi cannot continue," she said. "The Indian government must take swift action to ensure the safety of all of its citizens," she added.

The criticism stands in contrast to the reticence of the Trump administration.

Trump, asked at a news conference in New Delhi about the violence, said the issue was "up to India" and praised Prime Minister Narendra Modi's "incredible" statements on religious freedom.

The two leaders of the US Senate's pro-India caucus, Republican John Cornyn and Democrat Mark Warner, in a joint statement voiced support for the close US ties represented by Trump's visit but added: "At the same time, we are alarmed by the recent violence in New Delhi."

Representative Pramila Jayapal, an Indian-born left-leaning Democrat who has been outspoken in her criticism of Modi, called the developments "horrifying."

"Democracies should not tolerate division and discrimination, or promote laws that undermine religious freedom. The world is watching," she wrote on Twitter.

The clashes in Delhi, which have left at least 27 people dead, were triggered by protests against a citizenship law seen by critics as anti-Muslim and part of Modi's Hindu nationalist agenda.

Modi has called for calm, although witnesses said police did little to stop Hindu mobs. His government has previously vowed to weed out "infiltrators" from India, with Home Minister Amit Shah likening undocumented immigrants to "termites."