The FBI continues to investigate after four U.S. citizens were kidnapped in Matamoros last week.

The kidnapping occurred Friday after four Americans crossed into Matamoros in a white minivan with North Carolina license plates to buy medicine, according to a news release.

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“Shortly after crossing into Mexico, unidentified gunmen fired upon the passengers in the vehicle,” the news release stated. “All four Americans were placed in a vehicle and taken from the scene by armed men.”

One woman died in that shootout.

Andrés Manuel López Obrador, president of Mexico, said that Mexican authorities believe the kidnapping victims were targeted by mistake.

White House Press Secretary Karine Jean-Pierre addressed the kidnapping on Monday.

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“These sorts of attacks are unacceptable,” Jean-Pierre said. “Our thoughts are with the families of these individuals, and we stand ready to provide all appropriate consular assistance. U.S. law enforcement is in touch with Mexican law enforcement."

The FBI is offering a $50,000 reward for the return of the kidnapping victims and the arrests of those involved.