(CNN) Extreme overcrowding and children younger than 7 being held in custody for more than two weeks -- far longer than the allowed 72 hours -- are among the "urgent" issues discovered at Border Patrol facilities in unannounced visits by an internal government watchdog.

The unannounced inspections took place in early June in the Rio Grande Valley region of Texas, along the US-Mexico border. That area is the busiest sector for arrests on the southern border.

The report includes several photos that depict the extreme overcrowding, as well as standing-room-only conditions in some Border Patrol facilities, which are designed to be temporary holding facilities. However, over the past several months the length of time in custody has grown amid the ongoing influx of migrant families and children who turn themselves in to agents at the southern border.

For example, at the Centralized Processing Center in McAllen, Texas -- the main location for unaccompanied children in the region -- 165 children had been in custody longer than a week.

Investigators also found that, according to US Border Patrol custody data, roughly 30% of minors at the inspected facilities were held longer than the 72 hours permitted, including some children under 7 who had been held for more than two weeks awaiting transfer to Department of Health and Human Services custody.

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