A 16-year-old Guatemalan boy died while in US custody in South Texas on Monday — becoming the fifth migrant child to die since December, Customs and Border Protection said in a statement.

The unidentified teenager was apprehended after crossing the border near Hidalgo, Texas, on May 13, the agency said.

He was found unresponsive Monday morning during a welfare check at a CBP station in Weslaco, Texas.

The cause of death is unknown.

​”​The men and women of U.S. Customs and Border Protection are saddened by the tragic loss of this young man and our condolences are with his family,” acting Commissioner John Sanders said in the statement. “CBP is committed to the health, safety and humane treatment of those in our custody.”

​The boy was transferred to the Weslaco Border Patrol Station on Sunday from a processing center and was scheduled to be placed with an agency in the Health and Human Services for resettlement.​

Minors unaccompanied by a parent or legal guardian must be turned over to Health and Human Services within 72 hours, according to federal law.

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​The boy’s death is being reviewed by CBP’s Office of Professional Responsibility.

The Guatemalan government has been notified, the statement said.​

​A 2-year-old child died last week after being detained with his mother.

​In April, a 16-year-old boy died after being hospitalized in intensive care.

​Following the deaths of 7- and 8-year-old children in December, the Department of Homeland Security ordered medical checks of all children in custody.

All of the children were from Guatemala.

​With Post wires​