The American Civil Liberties Union of Arizona Wednesday sent a letter to the Department of Homeland Security accusing the department of not following civil rights laws when the agency detains children for entering the country illegally and alone.

Six agencies including the ACLU, the National Immigrant Justice Center and Americans for Immigrant Justice said children described their treatment in U.S. Customs and Border Protection detention centers as inhumane.

The complaint said more 116 unaccompanied immigrant children ages five to seventeen years old complained about treatment.

"One in four children included in this complaint reported some form of physical abuse, including sexual assault, beatings, and the use of stress positions by CBP officials," the report said. "More than half of these children reported various forms of verbal abuse and denial of medical care, including two young mothers whose infant children came back sick while detained in freezing temperatures."

Federal policy requires U.S. Border Patrol to transfer children to the Department of Health and Human Services within 72 hours of their arrest and detention. Then, the Office of Refugee Resettlement is responsible for family reunification, or getting the children to a family member in the United States or elsewhere.

Thousands of children are being held in a converted warehouse in Nogales, Ariz. after they were flown there from Texas.

The Department of Homeland Security responded to the allegations with a written statement saying mistreatment and misconduct are not tolerated.

"U.S. Customs and Border Protection is ensuring nutritional and hygienic needs are met, that the children are provided meals regularly and have access to drinks and snacks throughout the day and that facilities include toilets," CBP officials said in a statement. "In the face of overwhelming numbers of unaccompanied children crossing the border in South Texas, Border Patrol agents have taken extraordinary measures to care for these children while in custody and to maintain security in overcrowded facilities."

The report includes testimony from children collected before the spike in Central American unaccompanied minors overwhelmed the immigration system last month.

"The sheer volume and consistency of these complaints reflects longstanding, systemic problems with CBP policy and practices," the report said.