A 15-year-old unaccompanied migrant girl from Guatemala with a pre-existing medical condition died with her mother by her side in U.S. custody earlier this week. The teen's death is the fourth death of an unaccompanied migrant child in custody of U.S. Department of Health and Human Services (HHS) this year. 

In a statement Tuesday, HHS confirmed the girl's death. "Our heart goes out to the family at this difficult time," the department said. "(The Office of Refugee Resettlement) is working with them to provide comfort and assist with arrangements as appropriate."

According to information provided to Congress and obtained by CBS News, the teen arrived in the U.S. after crossing the southern border in May. 

The teen was hospitalized throughout her time in the custody of HHS, which cares for unaccompanied children who lack a legal immigration status. Shortly after her arrival in May, Customs and Border Protection (CBP) transferred her to HHS custody. 

She was already hospitalized in a pediatric intensive care unit in El Paso, Texas, because of a "significant, pre-existing illness," according to the notice sent to congressional officials.

As her health deteriorated last week, she was pronounced dead on July 10 as "a result of multi-organ failure due to complications of her underlying disease," the notice said. Officials said that the girl's mother and brother were with her at the time of her passing. 

Health officials said the Office of Refugee Resettlement wasn’t directing the teen’s day-to-day care at the time of her death. 

"While the child remained in ORR custody, medical treatment was provided according to the mother’s wishes and aligned with the recommendations of the hospital’s health care provider team," the statement said.

El Paso-based nonprofit Border Network for Human Rights released a statement criticizing federal policy on migrants and refugees. They also called on the federal government to develop "welcoming centers" along the U.S.-Mexico border that provides medical care, housing, food and legal services to migrants. 

"These incidents are part of an aggravated systemic failure that disregards the rights and well-being of refugees and migrants," said the group’s executive director, Fernando García, who acknowledged the child had pre-existing conditions and was getting care.

The other three deaths of unaccompanied migrant children in HHS custody this year include a 4-year-old Honduran girl who died this past March after being hospitalized for cardiac arrest in Michigan. 

In May, HHS disclosed the death of a 17-year-old Honduran boy who’d been housed in a shelter for unaccompanied minors in Florida. Officials at the time said the death likely was a result of an epileptic seizure. 

In June, a 6-year-old child who had been evacuated from Afghanistan following the Taliban takeover in 2021 died in HHS custody. He had a terminal illness.