A senior U.S. official told NBC News Sunday that immigration sweeps in line with an operation expected to target 2,000 immigrants over the coming days have begun at a slow pace.
Specific details, including the locations of the raids, were not immediately known.
Officials have said that the coordinated action will target about 2,000 people with final deportation orders in major cities, including San Francisco, Chicago, Los Angeles, New York and Miami.
The sweeps were expected to start Sunday, but New York City Mayor Bill de Blasio tweeted Saturday that the Immigration and Customs Enforcement agency had already taken action in New York.
Immigrant communities have been on edge since President Donald Trump's administration announced plans for the operation, inflaming the political debate over immigration. The American Civil Liberties Union filed a pre-emptive lawsuit Thursday that aims to protect asylum seekers. Activists held demonstrations and advocates coached immigrants on their rights.