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Staff members at a Phoenix-area shelter for unaccompanied migrant children allegedly physically abused three children, leading to the closure of the shelter, federal officials said. It was the latest in a series of incidents of alleged abuse involving staff members at shelters and children.

Southwest Key’s Hacienda del Sol shelter was shut down last Friday, but federal officials did not reveal the reason behind the closure until Tuesday.

The Texas-based federal contractor has fired the staffers involved in the Sept. 18 incident, the U.S. Department of Health and Human Services said in a statement.

The agency did not release additional details about the incident or how many staff members were involved.

The Maricopa County Sheriff’s Office did not immediately respond Wednesday to a request to locate the incident in its files. It was not immediately clear how many staff members were involved, or if any face possible criminal charges.

The Health and Human Service Department’s Office of Refugee Resettlement oversees children who crossed the border without their parents or have been separate from their parents due to the Trump administration’s previous zero-tolerance border policy.

“ORR has a zero-tolerance policy for all forms of abuse or inappropriate behavior at (migrant) care provider facilities and acts quickly to address any alleged violations of policy, including initiating employee disciplinary action, termination, or reporting to law enforcement agencies and all relevant licensing bodies,” the agency said.

The children were all relocated to the company’s other shelters within 10 days, The Arizona Republic reported.

Southwest Key is working to retrain staff, said Jeff Eller, a Southwest Key spokesman.

The closure comes after Arizona officials moved to revoke the licenses for Southwest Key after it missed a deadline to show that all employees passed background checks.

Arizona has seen numerous allegations of sexual abuse at its many shelters for immigrant children, including one made by the government of El Salvador, which said it received reports of three children, 12 to 17, who were sexually abused at unnamed shelters in Arizona.

Last month, a former youth care worker was convicted of sexually abusing seven teenage boys at a Phoenix-area shelter for immigrant children.

In August, authorities arrested a 32-year-old man on allegations that he had molested a 14-year-old girl at a Southwest Key facility the previous month.

Correction: A previous version of this story erroneously reported that some shelter staff members physically abused three children. Federal officials alleged the abuse took place but no charges have been filed.