India's foreign ministry has again defended a controversial citizenship register in Assam state after criticism from the United Nations, saying the almost two million people excluded from the list would not become "stateless".

India's ruling Bharatiya Janata Party (BJP) -- which also runs Assam, in the country's north-east -- had backed the National Register of Citizens (NRC) saying it was necessary to detect "foreign infiltrators".

Critics say it is being used by the BJP to push a Hindu nationalist agenda and marginalise the state's large minority of Muslims -- many who fled there when East Pakistan broke violently from Islamabad in 1971 to become Bangladesh.

Filippo Grandi, the UN High Commissioner for Refugees, had on Sunday called on New Delhi to avoid stripping people of their nationality, saying it "would be an enormous blow to global efforts to eradicate statelessness".

But foreign ministry spokesman Raveesh Kumar defended the process, saying the NRC "does not make the excluded person 'stateless'" and any decisions taken would be consistent with Indian law and its "democratic traditions".

"It (the NRC) also does not make him or her a 'foreigner', within the legal meaning of the term," Kumar said in a statement released late Sunday.

"For those who are not in the final list, (they) will not be detained and will continue to enjoy all the rights as before until they have exhausted all the remedies available under the law."

Assam, a poor and isolated state of 33 million, is largely surrounded by Bangladesh and has long seen influxes of migrants -- even during Britain's colonial rule.

But under the NRC, only those who can demonstrate they or their forebears were in India before 1971 can be included in the list.

Those left off have 120 days to appeal at so-called Foreigners Tribunals, and can also appeal their case through the courts.

A senior government official told reporters late Monday that some 500 tribunals would be up-and-running by December, and "even those cases who don't approach the tribunal will be scrutinised by the tribunal".

Story continues

He added that the government would provide legal support to those who can't afford to pursue their cases through the judicial system.

- 'No religious bias' -

Critics have said the NRC process reflects the BJP's goal to serve Hindus, with a large chunk of those excluded expected to be Muslims.

But there has been growing outrage among local BJP leaders, who claim many Bengali-speaking Hindus -- a key vote bank for the party -- had also been left off the list.

The official said claims that the list was biased against a particular religion "has absolutely no basis", adding that equal numbers of Hindus and Muslims were excluded.

"The entire process is fair and based on scientific methods. It is a non-discriminatory process and has absolutely no religious angle," the official, who asked to remain anonymous, told AFP.

He added that people who applied to be on the list did not have to declare their religious affiliation.

Home Affairs Minister Amit Shah is expected to visit Assam on Sunday and Monday, with the local BJP leadership set to call for his government to pass legislation to protect the rights of what it says are genuine citizens excluded from the list.

In January India's lower house passed legislation that would grant citizenship to people who moved to India as recently as six years ago -- as long as they are not Muslims.

It is not yet clear what will happen to people who have exhausted their legal avenues. In theory, they can be placed in one of six detention centres with a view to possible deportation to Bangladesh.

Bangladesh's home minister Asaduzzaman Khan told AFP late Monday that the NRC is an "internal matter of India", adding: "No Bangladeshi has moved to India after 1971."