The Maine Department of Corrections has reported another incident of unrest inside the youth prison, this time requiring backup from South Portland police.

Spokeswoman Anna Black said a small group damaged property inside the Long Creek Youth Development Center on Sunday night. She did not answer multiple questions Monday afternoon about that incident, including what caused the incarcerated youths to act out and how the staff contained the situation. No one was injured.

“However, the juveniles caused significant damage to the interior of the facility, including breaking windows and tearing apart classrooms, offices, and living spaces,” Black wrote in an email.

She said the department will work with internal investigators and the local prosecutor’s office “to identify potential charges for these juvenile offenders.”

Lt. Todd Berman said South Portland police officers responded to the prison Sunday night and stayed outside the building for six hours. The officers did not have any contact with incarcerated youths, he said, and he directed other questions to the Department of Corrections.

“Our involvement was just to make sure the fence was not breached,” he wrote in an email.

Black did not answer questions about why the department called local police for backup and whether the department has assisted at Long Creek in other instances.

The state recently hired the national Center for Children’s Law and Policy to conduct an independent review of recent altercations between staff and incarcerated youths. An advocacy group raised concerns about a dangerous tactic that was used to restrain young people during at least one of those incidents. Black did not answer a question Monday about whether officers on Sunday used those prone restraints, in which a person is held face down on the ground.

Based on those earlier incidents, the Cumberland County District Attorney’s Office is investigating at least two corrections officers at the youth prison for possible criminal charges, and the department was reviewing the actions of five others for possible policy violations. Black did not respond to a question about the status of those investigations.

Those developments have renewed calls to close the state’s last youth prison. On Friday, a dozen advocacy groups sent a letter with that demand and others to the governor’s office.

In response, department officials have repeatedly emphasized the increase in “high risk” juveniles at Long Creek. That assessment is based on the seriousness of the criminal charges and the need for behavioral intervention or mental health services. Those youths are placed in specific programs and housing at the prison.

Last month, corrections Commissioner Randy Liberty told legislators that 41 juveniles were detained or committed at Long Creek. Thirty-four, more than 80 percent, were classified as high risk. The commissioner didn’t provide a specific reason for that trend but said courts are more active than they were earlier in the pandemic.

Black did not provide updated numbers Monday. She said the department is working to restore programs that were paused because of the COVID-19 pandemic in hopes of curbing problems stemming from disengagement.

“Unfortunately, a small number of high-acuity residents, like those who intentionally destroyed property yesterday, continue to demonstrate aggressive, violent, destructive behavior,” she wrote.

Staff Writer Matt Byrne contributed to this report.