As the Trump administration continues to defend its “zero tolerance” immigration policy, which, since April, has separated more than 2,300 children from their parents at the border, ProPublica obtained an audio recording from inside a U.S. Customs and Border Protection facility. The recording captured the voices of kids as young as 4, crying for “Mami” and “Papá” as if those were the only words they knew.

The audio intensified the bipartisan outcry to put an end to the policy. But at a White House briefing Monday, Department of Homeland Security Secretary Kirstjen Nielsen blamed Congress, saying that until the nation’s immigration laws are rewritten, children will remain in detention centers as their parents face criminal charges for entering the country without permission, a move at the discretion of the administration.

Most concerning to the families being separated is what appears to be a lack of a plan to reunite the children with their parents. The little girl who can be heard crying in the video, 6-year-old Alison Jimena Valencia Madrid, had not been able to speak to her mother for days after they were separated, according to the girl’s aunt. Authorities at the shelter have warned the girl that her mother could be deported without her.