A 16-year-old unaccompanied immigrant died in federal custody Tuesday after days of intensive care.

Health and Human Services spokeswoman Evelyn Stauffer told NBC News that the boy died after “several days of intensive care,” although the cause of the boy’s death is not yet known. Stauffer said that the child was transferred from Immigration and Customs Enforcement to an Office of Refugee Resettlement shelter in Texas.

When the boy, who has not been identified, was transferred, “no health concerns were observed” by clinicians at the shelter. But the next morning, he “became noticeably ill” with a fever, chills, and headache. Shelter staff brought him to a hospital emergency room, where he was treated and released back to the shelter.

After his condition failed to improve, the boy was taken to an emergency room again.

“Later that day, the minor was transferred to a children’s hospital in Texas and was treated for several days in the hospital’s intensive care unit,” Stauffer said. “Following several days of intensive care, the minor passed away at the hospital on April 30, 2019.”

The death follows comments made in early April by Rep. Will Hurd, R-Texas, warning that federal authorities are overwhelmed by the influx of migrants. The congressman, whose district abuts 820 miles of the U.S.-Mexico border, also predicted that there might be a loss of life.

“April's going to be worse than March. You're going to see loss of life. You're going to see people that are in these conditions either die, or overrun a Border Patrol agent, or you're going to see massive destruction of property,” Hurd said.

Three migrants, two of whom were children, have died in federal custody since December.