Alexandria Ocasio-Cortez has denounced the US’s immigration and border authority as a “rogue agency”, a day after visiting a detention centre where children were kept in miserable conditions and the congressman said she personally felt unsafe.

Members of congress on Monday visited the controversial facility in Clint, Texas, operated by the border protection agency (CBP), and described witnessing horrendous conditions and staff who were uncooperative and unwelcoming.

Democratic congressman Joseph Kennedy said CBP staff tried to restrict what we saw, take our phones, block photos and video”. He added: “Atmosphere was contentious and uncooperative.”

Ms Ocasio-Cortez, who has long been a critic of the CBP and its enforcement arm, usually referred to as ICE, said she saw migrants drinking out of toilets, something the CBP denied.

On Tuesday, after ProPublica revealed the existence of a restricted Facebook group for current and former border agents that reportedly features jokes about migrant deaths, Ms Ocasio-Cortez doubled down on her criticism.

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“I can’t understate how disturbing it was that CBP officers were openly disrespectful of the Congressional tour,” she said on Twitter.

“If officers felt comfortable violating agreements in front of their *own* management & superiors, that tells us the agency has lost all control of their own officers.”

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She added: “When you pair 9,500 current + former CBP officers are part of a violently racist & sexually violent secret Facebook group, corroborating accounts of abuse [and] CBP couldn’t control their own officers for a Congressional tour, what else do you call that but a rogue agency?”

In an interview with CNN after her visit, she said: “In the last facility, I was not safe from the officers.”

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She did not elaborate on why she felt unsafe.