San Antonio, May 24 (RHC)-- The United States Department of Health and Human Services (HHS) has announced the death of a sixth migrant child in U.S. custody -- a young girl, who's death had gone previously unreported.

The 10-year-old girl was from El Salvador and had been detained by United States Border Patrol, an law enforcement group that has come under fire of late after the deaths of five other children, either while under their care or shortly after having been released.

On Monday, a 16-year-old Guatemalan boy named Carlos Hernandez died while under the care of Customs and Border Patrol. According to CBS News, the boy was diagnosed with Influenza A virus.

The Trump administration has been under fire for its treatment of migrants. From October 2018 to April 2019, nearly 293,000 people traveling as families were apprehended at the southern U.S. border -- a nearly four-fold jump over the same time frame the previous year.

Immigrant advocates say the administration’s policies, including making it more difficult for migrants to seek asylum at official ports of entry, contribute to making their journeys more arduous and drive migrants to seek out remote border outposts badly equipped to care for children.

Julie Linton, co-chair of the American Academy of Pediatrics’ Immigrant Health Special Interest Group, said she was concerned about sick children potentially being housed in bare-bones border protection facilities for extended periods of time.

“There certainly need to be conditions that do not include lying on a mat with a Mylar blanket on a floor that is cold, and cage-like fencing that extends to the ceiling,” she said on a conference call with reporters Monday. “We absolutely need pediatric health experts at the border.”