Washington — Accusing the government of staging a "concealment," a group of Democratic lawmakers is pressing the Trump administration for details on the case of a migrant girl whose September death in U.S. custody was not publicly disclosed until Wednesday by CBS News.

The Congressional Hispanic Caucus, comprised of Latino Democrats in the House and Senate, is demanding the Departments of Health and Human Services (HHS) and Homeland Security (DHS) provide Congress with more information on the death of Darlyn Valle — a 10-year-old girl from El Salvador with heart defects who died in HHS custody last fall.

"The death of a 10-year-old in the federal government's custody raises many questions about how we are treating families and children in our care," the Latino lawmakers wrote in a statement Saturday. "It is clear that DHS and HHS have set up a failed system that is often unprepared, neglectful and has led to inhumane conditions and even death."

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CBS News was the first to report that Darlyn, who had a debilitating heart condition, died in HHS custody last year. She was the first of six migrant children to die in U.S. custody — or soon after being released — in the past eight months.

In addition to Darlyn's death, five Guatemalan children apprehended by U.S. authorities near the southern border have died since December, three of whom were in CBP custody and one who died shortly after being released by the agency.

The Hispanic Caucus sent a letter Friday to the heads of DHS and the Office of Refugee Resettlement (ORR) — an agency within HHS in charge of caring for unaccompanied migrant minors.

In the letter, signed by caucus chair Rep. Joaquin Castro of Texas and first vice chair Rep. Ruben Gallego of Arizona, the lawmakers asked the Trump administration officials for the date when CBP first encountered Darlyn, the specific facilities where she was housed and the duration she remained in CBP custody before being transferred to HHS — a step which should take place within 72 hours of a minor's detention.

The two Democrats gave a June 7 deadline for their demands.

Mark Weber, a spokesperson for HHS, told CBS News that the girl had a history of congenital heart defects. Weber said when she entered the care of an ORR 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 said. "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."

Castro and Gallego asked in their letter if Darlyn was seen by a CBP clinician, and why she was kept in HHS custody for approximately seven months despite her grave medical condition.

Reiterating concerns raised by Castro when the death was first reported, the lawmakers demanded the administration identify the people and agencies who were informed of the girl's death and whether any member of Congress or congressional committee was briefed on it. They also requested a list of the children who have died in both DHS and HHS custody since the inception of both departments.

"It is critical that the Trump Administration respond to our questions immediately so Congress can work to address the current failed system in place," Castro and Gallego wrote.

On Thursday, Deputy CBP Commissioner Robert Perez — the second-highest ranking CBP official — told CBS News he's confident in the data his agency has publicly disclosed about the deaths of migrant children in U.S. custody. He stressed, however, that he could not speak for other federal agencies.

Spokespersons for HHS and DHS did not immediately respond to requests for comment.