Indian officials leading a charge to identify illegal migrants in the north-eastern state of Assam have said that the process “is not targeting Muslims”.
Opposition parties have accused the ruling Hindu nationalist Bharatiya Janata Party (BJP) of destroying lives.
Four million people were excluded from the National Citizens Registry (NCR) list, which was published on Monday.
NCR head Prateek Hajela told the BBC that those left out “are people from different religions and groups”.
The NCR is a list of people who can prove that they arrived in Assam prior to 24 March 1971, before neighbouring Bangladesh declared independence. The exercise, in a state with a history of communal violence, has stirred controversy.
Mr Hajela, who was appointed by the Supreme Court to handle the NCR, told BBC Urdu’s Shakeel Akhtar that the process “is about a specific date and has got nothing to do with religion, caste or race”.
But the opposition Congress party and some human rights groups have described it as an attempt to strip four million people, many of them Muslims, of their citizenship.
Critics have also alleged that the BJP government of Prime Minister Narendra Modi decided to publish the list for political purposes ahead of the general election next year.
However the Indian government has maintained the process is needed to root out illegal Bangladeshi migrants.
Home minister Rajnath Singh told the upper house of parliament that it was “fair and transparent” and that “no Indian citizen would be left out”.
Many Bengalis – a linguistic minority in Assam – are also worried they will be deported en masse.
But Mr Hajela said the list was not final and those excluded can appeal as well as submit “fresh documents” to claim citizenship in the coming months.