The FBI is searching for four U.S. citizens who have been kidnapped in Mexico, the U.S. Embassy in Mexico City said Sunday.

The American citizens crossed into Matamoros, in the northeastern state of Tamaulipas just south of Brownsville, Texas, in a white minivan with North Carolina plates on Friday, the embassy said.

“Shortly after crossing into Mexico, unidentified gunmen shot the passengers of the vehicle. The gunmen herded the four U.S. citizens into another vehicle and fled the scene with them,” according to the embassy.

The FBI is now asking for the public’s help in identifying who might be responsible and is offering a $50,000 reward, the embassy said.

Anyone with information can contact the FBI’s San Antonio Division at 210-225-6741.