Four U.S. citizens were assaulted and kidnapped in Mexico, the FBI said on Sunday. The gunmen reportedly opened fire on their vehicle near the border town of Matamoros in Tamaulipas state.

According to the FBI, the Americans were traveling from the border crossing town of Brownsville, Texas, on Friday, when their white minivan carrying North Carolina license plates was intercepted.

"All four Americans were placed in a vehicle and taken from the scene by armed men," according to a statement posted on the website of the U.S. Embassy in Mexico.

Ken Salazar, the U.S. Ambassador to Mexico, said in a statement Monday that an innocent Mexican citizen had died in the attack.

CNN cited a U.S. official who said the abduction of the Americans was a case of mistaken identity and that receipts found in the vehicle reveal that they were in Matamoros for medical procedures. There have been no reports of the identities of the four Americans.

The region has seen deadly fighting between factions of the Gulf drug cartel. Due to a recent uptick in violence, the State Department advised Americans against traveling to the region, citing the risk of crime and kidnapping.

"Criminal groups target public and private passenger buses, as well as private automobiles traveling through Tamaulipas, often taking passengers and demanding ransom payments," according to the State Department.

Mexican police issued a warning the same day of the alleged kidnappings, alerting parents to keep their kids home from school due to the recent violence in the city. There was no immediate indication that the warning was connected to the kidnapping.

A video posted to social media Friday appears to show several armed men loading bodies into a vehicle at what many assume is the scene of the kidnapping, but officials have yet to verify suspicions.

Matamoros was once considered a vacation destination for Americans and a hot spot for spring breakers. In the past 10 to 15 years, however, crime has all but eliminated the tourist industry.