MATAMOROS, MEXICO (WNCN) — A white minivan with North Carolina license plates was targeted by gunmen in the northern Mexico border city of Matamoros on Friday, FBI officials confirmed Sunday.

Four U.S. citizens in that vehicle were kidnapped after gunmen opened fire on the minivan, the FBI told CBS News on Sunday. Matamoros is a city currently in the middle of a drug cartel war involving local groups and outside influences, a U.S. security expert told Border Report.

The four had entered Matamoros, across from Brownsville, Texas, on Friday, the agency said. The FBI San Antonio Division office said the vehicle came under fire shortly after it entered Mexico.

“All four Americans were placed in a vehicle and taken from the scene by armed men,” the office said.

A post on Twitter Friday appears to show the moment they were kidnapped, CBS News reports. One woman, walking on her own, was forced into a white pickup truck. Men armed with long guns and wearing bulletproof vests are then seen dragging one person after another into the vehicle.

The conditions of the four are unknown as of Monday morning.

An alert issued Friday by the U.S. consulate in Matamoros addressed the media reports of an individual shot during what appears to be the same incident — warning government employees to steer clear. The alert also reminded U.S. citizens that this particular part of Mexico is considered a “Level 4: Do Not Travel” area, which is the highest-level warning in the U.S. State Department’s travel advisory system.  

The FBI is seeking help from the public, offering a $50,000 reward for the return of the victims and the arrest of the culprits.

CBS News and the Associated Press contributed to this report.