More than 14,000 children who arrived at the U.S.-Mexico border without a parent are in federal custody waiting to be released to adults within the United States, according to Biden administration officials.

Customs and Border Protection, the Department of Homeland Security agency that oversees Border Patrol, said Thursday afternoon that it has 4,500 children under the age of 18 being detained at its holding facilities up and down the 2,000-mile southern border. The Department of Health and Human Services Office of Refugee Resettlement has 9,562 children in its care as of Wednesday, two administration officials told reporters in a call Thursday.