India on Monday effectively stripped four million people in Assam of citizenship, sparking fears of mass deportations of Muslims from the northeastern state.
The draft National Register of Citizens (NRC), published on Monday, includes only those able to prove they were in Assam before 1971, when millions fled Bangladesh's war of independence into the state.
Critics say it is the latest move by the right-wing government of Prime Minister Narendra Modi to advance the rights of India's Hindu majority at the expense of its many minorities.
More than 30 million people had applied to be included on the list, of whom just over four million were excluded from the draft published on Monday, said Shailesh, the registrar general of India, who uses one name.
"No genuine Indian citizens need to worry as there will be ample opportunities given to them to enlist their names in the final NRC," he told a news conference in Assam's biggest city Guwahati.
He said those wishing to appeal could do so under "well-laid-down procedures" starting August 30. The definitive NRC is due to be finalised in December.
"We are going to provide assistance to anyone whose names are not included in the document and whoever wishes to file a claim and objection in this regard," Shailesh added.
Modi's Hindu nationalist government -- under whom extremist violence against Muslims has increased -- has said the list must be revised to root out illegal migrants.
Hundreds of thousands fled to India from Bangladesh during its 1971 war of independence from Pakistan. Most settled in Assam, which shares a long border with Bangladesh.
Rights groups have criticised the government's latest move, saying the deletion of people from citizenship rolls was similar to Myanmar's removal of rights and protections for its Rohingya community in 1982.
Avaaz, a US-based rights group, said Monday there was no effective appeal body and those left out would not have enough time to present their case.
"It's just Muslims who will likely have to go through a complicated, unfair appeal with no right to counsel, ending in no hope of staying if they lose," Ricken Patel, the executive director of Avaaz, said in a statement.
Assam, a state of 33 million people known for its lush tea estates, has for decades been racked by violence between indigenous tribes and settlers.
In one of the worst massacres, around 2,000 suspected migrants were butchered in a single day in Nellie in 1983. Nearly all were Muslim, and many were children.
In New Delhi, Home Minister Rajnath Singh also sought to allay fears about Assam.
"No coercive action will be taken against anyone. Hence there is no need to panic," Singh said in the upper house of parliament.
Satyen Garg, a home ministry official who was present at the Guwahati press conference, said there "was no question of sending anyone to detention camps based on the draft list".