Five days before the first government-imposed deadline to reunite migrant parents and children who were separated after crossing the Southwest border, immigration officials are mounting a round-the-clock effort involving hundreds of federal workers to bring the families together, a senior Trump administration official said Thursday.

Alex Azar, the secretary of Health and Human Services, said that nearly 3,000 separated children remained in the government's care, about 100 of whom were younger than 5. The youngest children must be reunited with a parent by Tuesday under a deadline imposed by a federal judge in San Diego. Older children must be returned to their parents by July 26 under the court's injunction.