Donald Trump was full of praise for Indian Prime Minister Narendra Modi's commitment to religious freedom despite strong criticism from both Christian and Muslim minorities in the country..

The US President's first official trip to India coincided with riots over new citizenship laws that grant amnesty to religious minority illegal immigrants - with the exception of Muslims - from Pakistan, Bangladesh and Afghanistan.

At least 25 people have been killed in clashes between Hindus and Muslims over the Citizenship Amendment Act (CAA), which Muslims say is discriminatory towards them and compromises India's claim to be a secular country. 

The Evangelical Fellowship in India has called the violence "reprehensible", and "the work of vested political interests and forces of hate".

Christians have long had their own concerns about Modi's government, with reports of an escalation in violence by Hindu nationalists against pastors, churches and believers since he came to power in 2014.

Trump told reporters that he had raised the issue of religious freedom with Modi and was impressed by what he had heard. 

"The prime minister was incredible on what he told me. He wants people to have religious freedom," Trump said at a news conference Tuesday.

"He said that, in India, they have worked very hard to have great and open religious freedom. And if you look back and you look at what's going on, relative to other places especially, they have really worked hard on religious freedom."

Joseph D'Souza, president of the All India Christian Council, said that Trump and Modi must work together to counter religious intolerance. 

"President Trump has made religious freedom for all a defining policy hallmark of his administration," he said. 

"Prime Minister Modi — as the leader of a nation of majority Hindus, 200 million Muslims and millions of Christians and other religious minorities — has the enormous responsibility of upholding religious freedom in the most religiously diverse nation in the world.

"Both President Trump and Prime Minister Modi need to counter religious and, yes, liberal extremism which is intolerant of diverse faiths.

"Religious freedom and peace are advantageous for economic growth and to fight extremism, and protecting this right could further strengthen U.S. and India's relationship.

"India and the United States have much to look forward to if our leaders champion these priorities."