Washington (CNN) The Department of Homeland Security was "not fully prepared" for the rollout of the Trump administration's "zero tolerance" policy at the US-Mexico border that resulted in the large numbers of family separations this summer, according to an internal report from the department's watchdog.

The new report from the DHS inspector general also says that Customs and Border Protection detained at least 861 unaccompanied children for extended periods beyond the legally allowed 72-hour time period.

One was held in a Rio Grande Valley facility for 25 days, the report says.

DHS also provided "inconsistent information," which led some parents to not understand that they would be separated from their children and unable to communicate with them.

The Justice Department Tuesday revealed that its inspector general has also opened a review into its role in the program.

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