The Pakistani authorities announced plans to expel more than one million Afghans living illegally in Pakistan, a sign of increasing hostility between the Pakistani government and Taliban authorities.

Hundreds of police officers flooded into a Karachi slum around midnight, surrounding the homes of Afghan migrants and pounding at their doors. Under the harsh glare of floodlights, the police told women to stand to one side of their homes and demanded the men present immigration papers proving they were living in Pakistan legally. Those without documents were lined up in the street, some shaking with fear for what was to come: Detention in a Pakistani prison and deportation to Taliban-controlled Afghanistan.

The police raid on Friday in Karachi, Pakistan’s largest city, followed an abrupt decision by the Pakistani authorities last week to deport the more than one million Afghan migrants living illegally in the country.

“Police entered every house without warning,” said Abdul Bashar, an Afghan migrant whose two cousins were among the 51 people who the police said were arrested during the neighborhood sweep. “The fear has left us restless, making it difficult for us to sleep peacefully at night.”

On Tuesday, Pakistan’s Interior Ministry announced that migrants residing illegally in the country had 28 days to leave voluntarily, and it offered a “reward” for information leading to their arrests once that deadline passed.

Though Pakistani officials say the crackdown applies to all foreign citizens, the policy is largely believed to be targeting Afghans, who make up the vast majority of migrants in Pakistan.