Roughly 8,000 immigrants being held in Border Patrol detention facilities in South Texas were subjected to "serious overcrowding" and prolonged detention, according to a report released Tuesday by the Department of Homeland Security's Office of Inspector General.

Photos of migrants in five Rio Grande Valley facilities show many packed into crowded standing-room-only cells and behind fences. Others are shown sleeping on the floor with aluminum blankets. More people cross into the U.S. illegally through the Rio Grande Valley sector than anywhere else along the U.S.-Mexico border.

"Specifically, when detainees observed us, they banged on the cell windows, shouted, pressed notes to the window with their time in custody, and gestured to evidence of their time in custody," the report said.

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The dangers facing migrants who cross the U.S.-Mexico border illegally were shown as photos of a father and daughter who drowned last month while trying to cross the Rio Grande were circulated around the world.

"The current situation on the Southern Border represents an acute and worsening crisis," Acting Inspector General Jennifer Costello said in a letter to Jim Crumpacker, the director of the Government Accountability Office-OIG Liaison Office. "Our immigration system is not equipped to accommodate a migration pattern like the one we are experiencing now."

The report comes as lawmakers and immigration-rights advocates have taken the Trump administration to task over alleged squalid conditions in which migrant detainees -- many of them children -- are living in. Many have tried pressuring the administration to release migrant families seeking asylum.

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At three facilities, government auditors said they observed children lacking full access to showers and a change of clothes. Some detainees were given wet-wipes in lieu of showers and many adults hadn't showered despite being held for as long as a month.

At two facilities, inspectors said children were not provided hot meals until the week they arrived. Around 3,400 people had been held longer than the 72 hours generally permitted under Customs and Border Protection standards. Of the 2,669 children detained by the Border Patrol, 826 had been held longer than 72 hours.

More than 50 children under the age of 7 were waiting to be moved to long-term facilities, the report said. A senior manager at one facility called the situation "a ticking time bomb."

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“The Inspector General’s report provides a shocking window into the dangerous and dehumanizing conditions that the Trump Administration is inflicting on children and families at the border," House Speaker Nancy Pelosi said in a statement. "This report is even more troubling after the discovery of the vile, crude comments made on social media by some of those in CBP responsible for caring for migrant families and children."

DHS did not immediately respond to a Fox News request for comment Tuesday evening.

The report also cited security incidents at multiple facilities. Some detainees have clogged toilets with the blankets and socks in order to be let out of their cells and some have refused to re-enter the cells after they had been cleaned.

Border Patrol agents made 132,887 apprehensions in May as a surge of Central American migrants continue to make the perilous journey north to claim asylum. Some congressional Democrats visited a migrant detention center in Clint, Texas on Monday, where lawyers said around 250 children were being detained in sub-par conditions.

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Rep. Alexandria Ocasio-Cortez, D-N.Y., has likened the detention facilities to concentration camps and claims women at one facility are being forced to drink "out of toilets."

On Monday, ProPublica reported on a secret Facebook group comprised of former and current Border agents joking about migrants deaths and making offensive comments about Hispanic members of Congress visiting a detention facility.

The Associated Press contributed to this report.