HARLINGEN, Texas (AP) — A migrant woman died in South Texas after spending less than a day in federal custody, U.S. Customs and Border Patrol announced Tuesday.

Border agents encountered the 29-year-old woman and her family in the Rio Grande Valley on Sunday afternoon, according to a statement from the agency. While she was in custody, she experienced a “medical emergency” and was treated by an on-site medical team and then taken to a hospital in Harlingen where she was pronounced dead, the agency said.

The woman spent less than 20 hours in custody, according to the statement. Agency guidelines state migrants must be processed within 72 hours.

No details were offered about the woman’s medical condition or her nationality.

An investigation, per agency protocol, is underway by the Office of Professional Responsibility. The Department of Homeland Security’s Office of Inspector General and the Harlingen Police Department were also notified.