A government investigation has uncovered human rights violations in U.S. immigrant detention centers.

A series of surprise inspections found immigrant detainees were subject to unnecessary strip searches, waited days for urgent medical care, and were placed in solitary confinement for minor infractions, among other issues, according to a report released yesterday by the Department of Homeland Security’s Office of Inspector General (OIG).

“Overall, the problems we identified undermine the protection of detainees’ rights, their humane treatment, and the provision of a safe and healthy environment,” the OIG report said.

Four of the five detention centers that the OIG visited during its investigation weren’t complying with Immigration and Customs Enforcement (ICE)’s basic standards for detainee care, according to the report.

For instance, at the Santa Ana City Jail—a California jail that houses immigrant detainees in addition to convicted criminals—the OIG found that all detainees were strip searched by guards when they first entered the facility, even though ICE guidelines reserve strip searches for situations when there are “specific and articulable facts” that suggest a detainee has contraband.

Detainees at Santa Ana and the Stewart Detention Center in Georgia said they had to wait days for medical treatment of painful illnesses, including a tooth infection and a knee injury.

And one detainee at an unnamed facility told the OIG that guards put them in solitary confinement for days as punishment for sharing coffee with another detainee.

This report comes just three months after the OIG found that ICE was putting detainees with mental health issues “at risk of harm” due to the agency’s liberal use of a form of solitary confinement, referred to as “segregation.” Earlier this year, POGO published an article detailing allegations in lawsuits around the country claiming that segregation is used to coerce detainees into performing unpaid or low paid work at detention facilities.

There are nearly 250 ICE detention centers spread across the United States. Their purpose is to hold people suspected of violating immigration laws while they await either deportation or immigration court hearings. As the OIG report noted, “All ICE detainees are held in civil, not criminal, custody, which is not supposed to be punitive.”

Even though ICE contracts out the management of most of its detention centers to private companies, all detention centers are supposed to follow standard ICE guidelines meant to ensure detainee wellbeing.

The report underscores the importance of robust and aggressive oversight of immigration detention facilities. Given the administration’s stated policy of expanding immigration enforcement and moves to increase the number of detention facilities while collapsing some oversight offices within ICE, greater oversight and transparency will be needed to prevent further abuses.

According to the report, the OIG chose to visit these five detention centers—all operated by companies or local governments, rather than by ICE itself—based on complaints it received via its hotline, as well as concerns from the public.

The OIG’s inspections “were unannounced so we could observe normal conditions and operations,” according to its report. When government watchdogs give prior warning that they will visit, it gives detention center operators the opportunity to hide problems before the watchdogs arrive.

Watchdog offices should utilize surprise inspections more often as an oversight tool. While gaining access to documents, for instance, is another critical method of overseeing agencies, nothing can replace seeing the real situation firsthand.