An 8-year-old boy from Guatemala died Tuesday while in U.S. custody, immigration officials announced, becoming the second child to die in such circumstances this month.

In a statement, Customs and Border Protection said the boy died shortly after midnight at the Gerald Champion Regional Medical Center in Alamogordo, N.M. The cause of death is unknown; he had received treatment at the hospital starting on Christmas Eve.

Immigration officials say an agent first “noticed that the child showed signs of potential illness” Monday and brought the boy and his father to the medical center, where the boy was diagnosed with a “common cold.”

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Prior to leaving the hospital, though, staff found a fever. They discharged the boy in the mid-afternoon with prescriptions for amoxicillin and Ibuprofen.

The Gerald Champion Regional Medical Center in Alamogordo, New Mexico., where the boy died Tuesday.

The Gerald Champion Regional Medical Center in Alamogordo, New Mexico., where the boy died Tuesday.

But later in the evening, the child “exhibited nausea and vomiting and was transferred back” to the facility for evaluation and treatment, CBP said, before dying around midnight.

Officials say the death is under investigation.

The Guatemalan government has been notified and is working with the boy’s father and family there.

“DHS has continued to see a dramatic increase in unaccompanied children and family units arriving at our borders illegally or without authorization,” CBP added in a statement. “Consistent with existing law, these individuals are held at federal facilities pending their removal or release into the interior of the United States with a notice to appear at a court hearing.”

The death came during an ongoing dispute over border security and with a partial government shutdown underway over President Donald Trump’s request for border wall funding. The White House did not immediately comment on the boy’s death Tuesday. CBP officers and the Border Patrol remain on the job despite the shutdown.

CBP promised “an independent and thorough review of the circumstances.”

The agency has not yet said when or where the father and son entered the United States or how long they were detained, saying only in its statement that the boy had been “previously apprehended” by its agents. CBP typically detains immigrants when they cross the border for short periods of time before releasing them or turning them over to U.S. Immigration and Customs Enforcement.

Alamogordo is about 90 miles (145 kilometers) from the U.S.-Mexico border at El Paso, Texas. Ruben Garcia, director of El Paso’s Annunciation House, said Tuesday that he had no reason to believe his shelter had served the family, but was waiting for further details about what happened.

A CBP spokesman declined to elaborate Tuesday, but said more details would be released shortly.

The body of a 7-year-old girl who died while in U.S. Border Patrol custody earlier this month – also from Guatemala — was flown to her home country Sunday ahead of burial in her home village.

In that case, Jakelin Caal and her father, Nery Caal, were traveling with a group of 163 migrants who arrived at the New Mexico border. After they were taken into custody Dec. 6, the father told a U.S. agent that the girl was sick and vomiting.

The father then signed a paper stating that Jakelin was in good health, but it was not clear how much he understood what it said. The form was in English, and agents read it to him in Spanish.

A bus carrying the two left the Antelope Wells port of entry for the Lordsburg station, roughly 90 minutes away. By then, according to a Customs and Border Protection statement, Jakelin’s temperature had reached 105.7 degrees. Emergency medical technicians had to revive her.

She was then flown to a hospital in El Paso, where she died the next day.

Caal’s death led to criticism of immigration officials by U.S. lawmakers, with five senior Democrats calling for a thorough review of their conduct. CBP announced new notification procedures in response to Jakelin’s death, which was not revealed until Dec.14.

Large numbers of Guatemalan families have been arriving in recent weeks in New Mexico, often in remote and dangerous parts of the desert.

Xochitl Torres Small, a Democrat who will represent the district starting in January, called for a thorough and transparent investigation into the children’s deaths and more medical resources along the border.

“This is inexcusable,” she said in a statement Tuesday. “Instead of immediately acting to keep children and all of us safe along our border, this administration forced a government shutdown over a wall.”

A spokeswoman for U.S. Rep. Steve Pearce, a Republican whose district along the U.S.-Mexico border includes Alamogordo, could not be reached Tuesday.

Fox News’ Amy Lieu, Sam Chamberlain and the Associated Press contributed to this report.