Texas Rep. Joaquin Castro, the chair of the Congressional Hispanic Caucus, accused the Trump administration of covering up the death of a 10-year-old migrant girl from El Salvador by failing to inform Congress and the American public. CBS News learned Wednesday that the girl, whose death in September 2018 had not been previously reported, had died in a hospital after entering government care in San Antonio.

"It's outrageous that another child has died in government custody and that the Trump administration didn't tell anybody," Castro told CBS News Wednesday night, referring to an exclusive report by CBS News that disclosed the girl's death.

The Texas Democrat, the twin brother of 2020 Democratic presidential candidate Julián Castro, said he had not seen "any indication" the Department of Health of Human Services (HHS), which had custody of the child when she died, briefed any lawmaker or congressional committee on the girl's death.

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"They covered up her death for eight months, even though we were actively asking the question about whether any child had died or been seriously injured," Castro added. Castro noted Democrats began asking the administration about migrant deaths in U.S. custody in the wake of the deaths of Jakelin Caal Maquin, 7, and Felipe Gómez Alonzo, 8, in U.S. Customs and Border Protection (CBP) custody.

He vowed to make "immediate inquiries" to HHS to get more information on the 10-year-old girl's death and called on the Justice Department to initiate an investigation into what is now a total of six deaths of migrant children who were apprehended by U.S. authorities near the southwestern border in the last eight months.

Castro also brushed aside a warning that acting Homeland Security Secretary Kevin McAleenan gave at a hearing earlier Wednesday. McAleenan told the Democratic-led House Homeland Security Committee that unless Congress approves more funding to deal with an unprecedented flow of migrant families heading toward the U.S.-Mexico border, it will be difficult for Homeland Security officials to prevent more deaths of migrant children in U.S. custody.

"We give them billions of dollars, and they want to use it on a wall instead of spending it to make sure that people don't die and that they can medically treat emergencies that migrants maybe come into or that their own agents may come into," Castro said.

HHS acknowledged to CBS News on Wednesday that the 10-year-old Salvadoran girl died in its custody on Sept. 29, 2018.

Mark Weber, an HHS spokesperson, said in a statement to CBS News that the girl had a history of congenital heart defects. Weber said when she entered the care of an Office of Refugee Resettlement (ORR), a HHS department, facility in San Antonio, Texas, on March 4, 2018, she was in a "medically fragile" state.

"Following a surgical procedure, complications left the child in a comatose state. She was transported to a nursing facility in Phoenix, Arizona for palliative care in May after release from a San Antonio hospital," Weber told CBS News. "On September 26, she was transferred to an Omaha, Neb., nursing facility to be closer to her family. On September 29, the child was transported to Children's Hospital of Omaha where she passed due to fever and respiratory distress."

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In addition to her death and that of Jakelin and Felipe in December, three other migrant children have died in the past eight months in U.S. custody or after being released by the government.

On Monday, Carlos Hernandez Vásquez, a 16-year-old boy who crossed into the U.S. without his parents, died at the Border Patrol station in Weslaco, Texas, after a nurse concluded he had the flu, a CBP official said. His death has drawn further scrutiny because he spent a week in the custody of CBP, which usually transfers children to HHS within 72 hours.

Last week, a 2 ½-year-old who was apprehended near El Paso in April died while with his family. According to CBP, the child was hospitalized for an unspecified illness three days after he was detained. He was later released with his family, who were given a notice to appear before an immigration judge.

In April, 16-year-old Juan de León Gutiérrez, who was apprehended by border patrol agents near El Paso, died in the custody of HHS. According to the Guatemalan Foreign Ministry, Gutiérrez died from complications from an infection in his brain's frontal lobe.

Graham Kates and Angel Canales contributed reporting.