Intensifying its enforcement in so-called sanctuary cities across the country, Immigration and Customs Enforcement has begun 24-hour-a-day surveillance operations around the homes and workplaces of immigrants living in the country illegally. The agency plans to deploy hundreds of additional officers in unmarked cars in the coming weeks to increase arrests in cities where local law enforcement agencies do not cooperate with federal immigration enforcement.

ICE leadership has requested at least 500 special agents who normally conduct long-term investigations into dangerous criminals and traffickers to join the enhanced arrest campaign rolling out in sanctuary cities, according to an internal e-mail reviewed by the New York Times.

The request follows an earlier decision, made public last month, to deploy elite tactical BORTAC agents — immigration SWAT teams that are normally assigned to risky border smuggling, rescue and intelligence operations — to help arrest and deport immigrants in sanctuary cities.

The expanded surveillance operations and added manpower are the latest intensification in a conflict between the Trump administration and cities that refuse to help with deportations, including Boston, New York, Detroit, Chicago, San Francisco, Los Angeles, Atlanta, New Orleans and Newark, N.J. The effort began last month and will run through Dec. 31, according to the internal e-mail, which says the initiative is called Operation Palladium.

The latest directive is simple: Arrest as many immigrants living in the country illegally as possible, and “flood the streets,” as one official involved said his bosses had put it.

The Trump administration’s renewed focus on sweeping up immigrants living in sanctuary jurisdictions illegally comes after years of efforts to persuade those local governments to turn over anyone released from prison or jail who is in the United States illegally.

Local leaders in those communities often argue that doing so could make their cities less safe by discouraging people from cooperating with the police.

Because immigration law violations are civil infractions rather than criminal ones, the officers deployed in the expanded ICE operations cannot, in most cases, obtain warrants to forcibly enter places where their subjects are hiding.

Instead, ICE officers are embarking on the aggressive surveillance campaign, which involves closely watching some individuals for more than 12 hours a day in the hopes of arresting them outside their homes or workplaces.

An ICE official directly familiar with Operation Palladium said the enforcement actions were to take place in spurts in different cities to avoid intense coverage by the national media that could cause people wanted for deportation to hole up in their homes for days or weeks.

“If there’s no cooperation, that’s not going to stop ICE from doing its job,” said Henry Lucero, the top government official overseeing the division of ICE that conducts street arrests.