WASHINGTON — Overcrowded, squalid conditions are more widespread at migrant centers along the southern border than initially revealed, the Department of Homeland Security’s independent watchdog said Tuesday. Its report describes standing-room-only cells, children without showers and hot meals, and detainees clamoring desperately for release.

The findings by the Department of Homeland Security’s Office of Inspector General were released as House Democrats detailed their own findings at migrant holding centers and pressed the agency to answer for the mistreatment not only of migrants but also of their own colleagues, who have been threatened on social media.

[Read the report from inspector general’s office.]

In June, inspectors from the department visited five facilities in the Rio Grande Valley of Texas, and found children had few spare clothes and no laundry facilities. Many migrants were given only wet wipes to clean themselves and bologna sandwiches to eat, causing constipation and other health problems, according to the report. Children at two of the five facilities in the area were not given hot meals until inspectors arrived.

Overcrowding was so severe that when the agency’s internal inspectors visited some of the facilities, migrants banged on cells and pressed notes to windows begging for help.