The federal government has placed thousands of unaccompanied immigrant children in the homes of sponsors, but last year it couldn’t account for nearly 1,500 of them.

Steven Wagner, a top official with the Department of Health and Human Services, disclosed the number to a Senate subcommittee last month while discussing the state of the Office of Refugee Resettlement (ORR) that oversees the care of unaccompanied immigrant children.

Wagner is the acting assistant secretary for the Administration for Children and Families, which is part of the Department of Health and Human Services. ORR is a program of the Administration for Children and Families.

CNN reported earlier this month that, in his testimony, Wagner said during the last three months of 2017, the ORR lost track of nearly 1,500 immigrant children it had placed in the homes of sponsors.

Wagner’s statement has attracted more attention amid reports that immigrant children are being separated from their parents at the US border.