Immigrants and advocates had been bracing for the arrests, which Trump last warned of on Friday, saying he wanted agents “to take people out and take them back to their countries.” But federal law enforcement officials said they worried that the unusual public disclosure of the plan endangered officers and threatened their effectiveness.

Trump has vowed repeatedly to deport “millions” of people who are in the United States illegally, and the long-planned blitz aims to target families who entered the country recently and have received deportation orders. U.S. Immigration and Customs Enforcement has for years regularly arrested and removed immigrants who a judge has deemed should be deported after court hearings.