A waste picker from a Delhi slum, who said he had been deported with his pregnant wife and son. A rice farmer in Assam, in India’s northeastern corner, who said his mother had been detained by police for weeks. A 60‑year‑old shrine attendant in the western state of Gujarat, who said he had been blindfolded, beaten by the police and then put on a boat.

All have been caught up in a widening crackdown on migrants that the Indian government has justified as a national security imperative. Rights groups say the crackdown, which intensified after a terrorist attack in Kashmir in April, has become an increasingly arbitrary campaign of fear against Muslims in India, especially those whose language might mark them as outsiders. Most of those detained in the raids live hundreds of miles from Pakistan, which India has blamed for the attack.

Thousands of Indian Bengali-speakers, most of them Muslims, have been rounded up, detained or expelled to Bangladesh. Many of them are from West Bengal, an eastern Indian state where Bengali is the main language; for decades, young people from the state have migrated to big Indian cities elsewhere for work.

Several million undocumented Bangladeshis are thought to live in India, entering — legally or illegally — through the porous border that divides the two nations. Indian states have carried out raids on neighborhoods with dense concentrations of Bengali speakers, saying they had evidence of undocumented immigrants there. (Bengali, an official language of both India and Bangladesh, is spoken by tens of millions of people on both sides of the border.)

Since mid-July, authorities in Gurgaon, a satellite city of the capital, New Delhi, have conducted what they call a verification drive, intended to identify illegal immigrants.

The police in Gurgaon have detained and then released hundreds of people with documents showing they lived legally in India, according to local media reports. Hundreds of mostly poor Bengali speakers, the reports said, preemptively fled the city after the drive began, worried they would be picked up by the police at any moment.