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The four Americans who were kidnapped by gunmen just across the southern border on Friday were traveling to Mexico for a medical procedure, according to several media reports.

Family members told CNN that the group of tight-knit friends was traveling from South Carolina to Mexico so that one could undergo a medical procedure, but they never made it to the appointment.

Mexican President Andrés Manuel López Obrador similarly confirmed on Monday that the group “crossed the border to buy medicine, and there was a confrontation between groups, and they were detained.”

The group, which was traveling in a white minivan with North Carolina license plates, was shot at by gunmen soon after crossing into Matamoros, Tamaulipas, Mexico, on Friday evening, according to the FBI’s San Antonio Division. The four Americans were then placed in a vehicle and taken from the scene.

A Mexican citizen also died in the attack, U.S. Ambassador to Mexico Ken Salazar said.

“We have no greater priority than the safety of our citizens — this is the US government’s most fundamental role,” Salazar added. “US law enforcement officials from numerous agencies are working with Mexican authorities at all levels of government to secure the safe return of our compatriots.”