PHOENIX — Claiming "systemic abuse" of children who arrive in this country alone, immigrant rights groups demand this morning the Department of Homeland Security conduct an immediate investigation.

The 25-page complaint alleges that children whose stories they have detailed "have been subjected to various forms of abuse, harassment and other harms at the hands of the Border Patrol."

There also are allegations of denial of medical care, including a child whose asthma medication was confiscated while she suffered multiple asthma attacks.

"Children consistently reported being held in unsanitary, overcrowded and freezing-cold cells, and roughly 70 percent reported being held beyond the legally mandated 72-hour period," the complaint says.

That last point, at least, already has been corroborated by senior officials in the Obama administration. They conceded on Monday that the sudden influx of unaccompanied minors has overwhelmed the system, meaning children cannot be processed and turned over to the Department of Health and Human Services within that 72-hour window.

But the complaint says the problems cited are not new — and not simply the result of the recent flood of unaccompanied minors.

"The sheer volume and consistency of these complaints reflects longstanding, systemic problems with CBP policy and practices," according to the groups which filed the complaint. They include the National Immigrant Justice Center, Esperanza Immigrant Rights Project, Americans for Immigrant Justice, the Florence Immigrant Rights & Refugee Project and the American Civil Liberties Union Border Litigation Project.

"Unfortunately, the abuse of unaccompanied children by U.S. immigration officials is not a new phenomenon," the complaint alleges, with the groups saying it has "documented civil rights violations" by Border Patrol and other federal immigration agencies for years. Those reports, the groups said, do not result in action against agents who break the law, with many complaints never properly investigated.

"By failing to meaningfully investigate or otherwise respond to consistent reports of systemic abuse, Department of Homeland Security has demonstrated a continuing disregard for the civil and human rights of unaccompanied immigrant children," the complaint says.