Five immigrant rights groups filed a complaint Wednesday accusing US border officials of participating in the systemic abuse of unaccompanied migrant children detained near the southwest border, including physical and sexual abuse, painful shackling and denial of adequate food and water.

The complaint details alleged abuse and mistreatment suffered by 116 children detained by US Customs and Border Protection officials. One in four children said they experienced physical abuse, including kicking, beating and forced stress positions. More than half reported verbal abuse, including taunts, death threats and racist or sexually charged comments. A majority said they were held for longer than seventy-two hours, the maximum time permitted before CBP officials are required to transfer custody to the Office of Refugee Resettlement.

Cases of abuse and mistreatment are described in graphic detail. A sixteen-year-old Central American girl said agents “violently spread her legs” while searching her, touching her genitalia and making her scream. A seventeen-year-old boy detained near Hidalgo, Texas said he was forced to maintain a stress position for twenty minutes as punishment for laughing. A seventeen-year-old rape survivor who fled Guatemala said she was repeatedly harassed by CBP officials; one allegedly told her, “We’re going to put you on a plane, and I hope it explodes. That would be the happiest day of my life.”

Most of the children reported being held in frigid holding cells, nicknamed hieleras, Spanish for “freezers.” Interviewees described squalid conditions at these sites, including severe overcrowding and scarce food and water. In at least one facility, up to 100 children share a single toilet, exposed in plain view to everyone, including CBP officers.

The complaint was filed with the Department of Homeland Security’s Office of Civil Rights and Civil Liberties, as well as the Office of the Inspector General. Its authors include the National Immigrant Justice Center, Esperanza Immigrant Rights Project, the American Civil Liberties Union of Arizona and Americans for Immigrant Justice.

In response to the complaint, CBP spokesperson Michael Friel said, “While in temporary custody, CBP strives to protect unaccompanied children with special procedures and safeguards…. Mistreatment or misconduct is not tolerated.”

The accusations come as immigration officials struggle to deal with unprecedented influx of migrant children across the US-Mexico border, deemed an “urgent humanitarian crisis” by President Obama. CBP officials have apprehended more than 47,000 unaccompanied children since October, nearly double the number from last year. Experts tie the surge of child migrants to increasing gang violence in Central America, including Honduras, Guatemala and El Salvador. Human and civil rights advocates say the recent influx of migrant youths highlights the need to address CBP’s systemic abuse.

“Children are fleeing untenable conditions in their home countries, including pervasive violence and persecution, and are often re-victimized in transit to the United States,” said Joseph Anderson, director of litigation for Americans for Immigrant Justice, in a statement. “We need to ensure that these children are treated with dignity and respect and afforded all applicable legal protections while they are in US custody.”

CBP, the largest law enforcement agency in the nation, is no stranger to accusations of misconduct. The agency removed its top internal affairs chief this week over mounting criticism that he routinely refused to investigate use-of-force allegations.

The groups involved with the complaint are calling for immediate redress and reform, including enhanced oversight through an independent body and the creation of short-term detention standards, as well as a streamlined complaint process. They are also asking for an investigation into the abuse cases described in the complaint.

“This complaint is further proof that the CBP is an agency in need of massive reform,” said James Lyall of the ACLU Border Litigation Project. “This should be the final straw.”