President Arif Alvi has condemned the burning of a mosque in New Delhi's Ashok Nagar area during the violent clashes over India's new citizenship law on Tuesday.

Protests against a contentious citizenship law began on a smaller scale on Sunday but escalated on Monday — as US President Donald Trump started his two-day trip to India — and Tuesday into running battles between Hindus and Muslims in New Delhi’s north-east, where rioters armed with stones, swords and even guns were out in force.

By Wednesday, the death toll from the violence increased to 20 and more than 200 people were reported injured.

A video — verified by AFP — circulating on social media on Tuesday showed men ripping off the muezzin's loudspeaker on top of the mosque's minaret and placing a Hanuman and an Indian flag. The Wire reported that a mob shouting “Jai Shri Ram” and “Hinduon ka Hindustan” paraded around the mosque as it burned. Copies of the Holy Quran were also burnt during the attack, AFP reported.

On Wednesday morning, AFP said that people were seen cleaning out the blackened and trashed interior of the mosque.

President Alvi, in a tweet late Tuesday night, said: "Another update of the disgraceful act. Vandalising a mosque! It seems to be a reminder to Muslims of the Babri Masjid episode.

"I think secular forces within India should rise against such barbaric actions."

Read: PM Imran urges international community to 'act now' on deadly violence against Muslims in India

'Tragic failure of moral leadership'

Several lawmakers in the United States also raised concerns over the violence in New Delhi.

“It is important to strengthen relationships with democratic partners like India,” said Elizabeth Warren, the Democratic Party’s contender for upcoming US presidential elections.

“But we must be able to speak truthfully about our values, including religious freedom and freedom of expression – and violence against peaceful protesters is never acceptable.”

United States Congresswoman Pramila Jayapal, while expressing shock over the violence, said that it is a “deadly surge of religious intolerance".

“Democracies should not tolerate division and discrimination, or promote laws that undermine religious freedom. The world is watching,” she tweeted.

Last year, Jayapal had introduced a United States’ Congressional resolution asking India to end the restrictions on communications in Jammu and Kashmir, and reserve religious freedom for all residents.

“This week, Trump visited India but the real story should be the communal violence targeting Muslims in Delhi right now,” tweeted United States Democratic Congresswoman Rashida Tlaib.

“We cannot be silent as this tide of anti-Muslim violence continues across India.”

US lawmaker Alan Lowenthal — while tagging a news report — said it was a “tragic failure of moral leadership”, and said that people must “speak out in the face of threats to human rights in India”.

The United States Commission on International Religious Freedom (USCIRF) said reports of “deadly mob violence targeting Muslims in New Delhi” were alarming and tweeted that it “urges the Modi government to rein in mobs and protect religious minorities and others who have been targeted".