This story has been updated with the most recent statement by the Department of Health and Human Services (HHS)

Washington — Thousands of migrant children allegedly suffered sexual abuse while in U.S. government custody over the past four years, according to Department of Health and Human Services (HHS) documents released Tuesday by Florida Democratic Rep. Ted Deutch.

According to the documents, over a thousand allegations of sexual abuse against unaccompanied minors in HHS custody were reported to federal authorities each fiscal year since 2015. In total, between October 2014 and July 2018, 4,556 sexual abuse complaints were reported to the Office of Refugee Resettlement (ORR) — an agency within HHS in charge of caring for unaccompanied migrant minors.

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An additional 1,303 complaints were received by the Justice Department between fiscal years 2015 and 2018, but it's unclear whether these complaints overlap with those reported to ORR.

The documents offer a fragmented portrayal of the allegations of sexual abuse. The overall numbers of the allegations reported to ORR do not reveal specific information about the alleged perpetrator, who may be someone unknown to the child, another unaccompanied minor or a caregiver in a U.S. facility. On the other hand, the data of allegations reported to the Justice Department does provide specific information about who the alleged perpetrator was.

The documents reveal that over the past four fiscal years, in 178 cases reported to the Justice Department, adult caregivers at U.S. facilities were reported to have sexually abused migrant minors. More specifically, there were 49 allegations of sexual abuse involving adult caregivers in U.S. facilities reported to the Justice Department in both fiscal years 2017 and 2018.

"The gravity here is a systematic concealment of children being sexually abused, children being exposed to those kinds of acts," Democratic California Rep. Lou Correa told CBS News Tuesday afternoon, as he left a House Judiciary Committee hearing on the Trump administration's family separation policy near the southwestern border.

Correa said the government has the legal responsibility to prevent children under its custody from being abused or harmed and accused the Trump administration of a "systematic cover up." The California Democrat said the government documented these allegations but failed to elevate them to the highest levels of the administration. It was only when House Democrats requested the documents in January that the government revealed the statistics, he added.

"We're supposed to have transparency, we're supposed to work and make things better. If you make mistakes, you fess up to that and you move on," Correa said. "But to cover up something like this — child abuse — is just beyond my imagination."

One of the documents, which details the allegations of sexual abuse by adult facility staff during fiscal years 2015 and 2016, describes incidents in which unaccompanied minors reported they had been shown pornographic material, forcibly kissed, or inappropriately touched or fondled. Most of the accused facility members were immediately removed from duty and some cases were referred to law enforcement, according to the document. Some facility staff members were terminated, but others were reinstated.

According to an ORR memorandum, the agency began collecting sexual abuse data on unaccompanied minors in its custody in October 2014. Per ORR policy, care providers have to report allegations of sexual abuse, sexual harassment and retaliation against allegations no later than four hours after learning of the alleged incidents.

An HHS official told CBS News that, under agency policy, providers have have to report all allegations of sexual abuse to ORR, state and child protective services, the Office of Inspector General for HHS and the FBI. Additionally, the official said, providers must suspend employees accused of sexual abuse from duties that allow them access to minors.

In a statement to CBS News Tuesday afternoon, HHS spokesperson Caitlin Oakley said background checks for all facility employees are mandatory and that the safety of migrant youth is the agency's "top concern."

"These are vulnerable children in difficult circumstances, and ORR fully understands its responsibility to ensure that each child is treated with the utmost care," Oakley added. "When any allegations of abuse, sexual abuse, or neglect are made, they are taken seriously and ORR acts swiftly to investigate and respond."

Late Tuesday evening, HHS released a new statement accusing Deutch of mischaracterizing the data, particularly in saying that federal staff members from ORR were the ones being accused of sexual abuse.

"This was totally false," Jonathan Hayes, Acting ORR director said in the statement. "His knowing mischaracterization of the data—and his impugning of the ORR federal staff—was an immoral and indecent insult to all of the career civil servants who are dedicated to ensuring the health, safety, and welfare of the children in the unaccompanied alien children (UAC) program."

In his statement, Hayes was likely referring to Deutch's comments during Tuesday morning's House Judiciary Committee hearing, in which the Florida Democrat revealed the documents obtained from HHS. "These documents tell us there was a problem with adults, employees of HHS, sexually abusing children," Deutch said during the hearing.

But Hayes pointed out that of the 178 allegations over four years of sexual abuse against migrant youth by facility personnel, "none of the allegations involved ORR federal staff."

All care facilities for unaccompanied minors operate under both state and federal oversight.

Correa, the California Democrat, said his party will continue to hold the administration accountable on these allegations. He said the House Judiciary Committee, which he is a member of, is actively "looking" at several questions left unanswered by the documents, including the disparity between the number of sexual abuse allegations reported to ORR and the number reported to the Justice Department.

"It is my hope that they understand that there's a new sheriff in town — and oversight is not a joke," Correa added.