GENEVA — The United Nations’ top human rights official on Monday entered the mounting furor over the Trump administration’s policy of separating undocumented immigrant children from their parents, calling for an immediate halt to a practice he condemned as abuse.

United States immigration authorities have detained almost 2,000 children in the past six weeks, which may cause them irreparable harm with lifelong consequences, said Zeid Ra’ad al-Hussein, the United Nations high commissioner for human rights.

He cited an observation by the president of the American Association of Pediatrics that locking the children up separately from their parents constituted “government-sanctioned child abuse.”