The acting commissioner of the US Customs and Border Protection agency has resigned from his position, according to a copy of a message to his employees.
John Sanders's resignation, announced on Tuesday, followed an outcry over the treatment of migrant children in one of the agency's facilities near the border with Mexico.
Lawyers said 250 children had been held for weeks in squalid conditions at an overcrowded border patrol station in Clint, Texas. According to the lawyers, the children were not given adequate food and water and often went long periods of time without a shower.
Although some of the children were relocated to other centres, the Associated Press reported on Tuesday more than 100 children were moved back to the facility.
The reports highlighting the conditions of the facility has renewed criticism from immigrant rights activists and Democrats of Republican President Donald Trump's hardline immigration policies.
Six children have died since late last year after being detained by the agency along the US-Mexico border.
Neither the federal official speaking to the New York Times, who first broke the story about Sanders's departure, or Sanders in his message to employees said whether the resignation was connected to criticism over the agency's handling of the substantial influx of migrant families along the US-Mexico border.
Rights groups cautioned that Sanders's resignation would not end the mistreatment of immigrants in border centres.
"This is an intentionally racist and violence region who've target immigrants since they took office, RAICES, an immigrants rights organisation said. "They need to be held accountable."
Sanders pushed Congress to pass $4.5bn in humanitarian funding to address the crisis caused by the migrant surge.
On Tuesday, US House Democrats said they plan to approve the funding, but the measure has drawn a veto threat from Trump.
"This week we have to solve the humanitarian crisis," House of Representatives Democratic Caucus Chairman Hakeem Jeffries told reporters, predicting that the funding package would pass the House with a "strong Democratic vote".
Democrats were rushing to add language before the vote to mandate better health and nutrition standards at border facilities.
The changes were being made after some expressed alarm that not enough was being done to improve conditions at the border, where the number of migrants and asylum seekers apprehended surged in May to the highest level since 2006.
Sanders has been acting as the agency's chief since April when Trump appointed the former commissioner Kevin McAleenan as homeland security secretary.
Previously, Sanders was the agency's chief operating officer and had also been the Transportation Security Administration's chief technology officer.
In his resignation letter, obtained by Axios, Sanders said wound step down on July 5.