US President Donald Trump and First Lady Melania Trump listen to Indian Prime Minister Narendra Modi (left) during their visit to Gandhi Ashram in Ahmedabad on Monday. Trump will visit the Taj Mahal in Agra and hold official meetings in New Delhi during his trip. Photo: AFP

US President Donald Trump and Indian Prime Minister Narendra Modi have agreed to "promptly" conclude ongoing trade talks that they hope can lead to the first phase of a bilateral US-India trade deal, the White House said.

The statement follows Trump's visit to India on Monday and Tuesday, during which the US president clinched the sale of $3 billion of military equipment to India.

"They [Trump and Modi] agreed to promptly conclude the ongoing negotiations, which they hope can become phase one of a comprehensive bilateral trade agreement that reflects the true ambition and full potential of the bilateral commercial relations," the White House said late on Tuesday, giving no details on what would be included in the deal between the two sides.

Earlier on Tuesday, Trump criticized India for its high tariffs.

"India is probably the highest tariff nation in the world," he said.

Ahead of the president's trip, negotiators from the two sides wrangled for months to narrow differences on farm goods, medical devices, digital trade and new tariffs.

"If the deal happens with India it will be at the end of this year and if it doesn't happen then we will do something else," Trump said on Tuesday.

He said the US wanted to be treated fairly and given reciprocal access to India's market.

Separately, his trip coincided with violent clashes in New Delhi between Hindu and Muslim groups over a new citizenship law in India.

Modi called for calm Wednesday after the capital's worst sectarian violence in decades left at least 22 people dead and called for a military curfew.

This week's battles have seen mobs armed with swords, guns and acid raze parts of a northeastern district of the Indian capital.

The clashes, which also left almost 200 injured, were triggered by protests against a citizenship law seen by many critics as anti-Muslim and part of Modi's Hindu nationalist agenda.

They exploded into brutal violence on Monday and Tuesday, with residents forced to flee their homes after seeing dwellings destroyed, a mosque attacked and a tyre market and two schools set ablaze.

"I appeal to my sisters and brothers of Delhi to maintain peace and brotherhood at all times. It is important... calm and normalcy is restored at the earliest," Modi tweeted on Wednesday.

Delhi's chief minister, Arvind Kejriwal, a political opponent, called for the army to be deployed and for a curfew to be imposed.

"Police, despite all its efforts, [are] unable to control situation and instill confidence," Kejriwal tweeted.

Sunil Kumar, director of the hospital where many of the wounded people were taken, told AFP on Wednesday that almost 60 had gunshot injuries and that 16 new patients were admitted on Wednesday.