An autopsy performed on the 8-year-old Guatemalan boy who died in U.S. custody early Christmas Day shows he had influenza, New Mexico authorities said Thursday.

More tests need to be done before a cause of death can be determined for Felipe Gomez Alonzo, the New Mexico Office of the Medical Investigator said in a statement.

Felipe died at a New Mexico hospital after suffering coughing, vomiting and a fever, authorities said.

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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.”

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

But later in the evening, the child “exhibited nausea and vomiting and was transferred back” to the facility for evaluation and treatment before dying around midnight, U.S. Customs and Border Protection officials said.

GUATEMALAN BOY, 8, DIES IN US BORDER PATROL CUSTODY

Officials said the death remained under investigation, with the CBP promising "an independent and thorough review of the circumstances."

The boy's father had taken his son to the border after hearing rumors that parents and their children would be allowed to migrate to the U.S., the boy's stepsister said two days after the boy's death.

Felipe's death marked the second death of a migrant child under U.S. custody. A Guatemalan girl, Jakelin Caal, 7, died on Dec. 8. Both deaths are under investigation.

In response to the two migrant children's deaths, Homeland Security Secretary Kirtsjen Nielsen was planning to visit the U.S.-Mexico border region Friday and Saturday, Politico reported, citing a department spokesperson Katie Waldman.

Nielsen said this week that she'd "directed a series of extraordinary protective measures," including new medical screenings, for detained migrant children and that she would visit the border, according to the report.

Nielsen will travel Friday to El Paso, Texas, and Saturday to Yuma, Ariz., Waldman said in an email to Politico.

She will also personally review her department's care of migrant children, Bloomberg News reported.

“This tragedy, the death of a child in government custody, is deeply concerning and heartbreaking,” Nielsen in a statement, according to the report. “Moving forward, all children will receive a more thorough hands-on assessment at the earliest possible time post-apprehension -- whether or not the accompanying adult has asked for one.”

CBP ordered new medical tests on all children under its custody after the Guatemalan boy’s death, the agency said in a statement Wednesday, Bloomberg reported.

The directive will mean secondary medical checks on children under the agency’s care, including unaccompanied minors and those who arrive as part of a family unit, with the order focusing on children under 10, CPB Commissioner Kevin McAleenan said in the statement obtained by the news outlet.

“This is a tragic loss. On behalf of U.S. Customs and Border Protection, our deepest sympathies go out to the family," McAleenan said in a statement Tuesday.

Fox News' Greg Norman and the Associated Press contributed to this report.