(CNN) -- Four US citizens were assaulted and kidnapped after crossing the border into northeastern Mexico on Friday, according to the FBI, which is working to locate the missing Americans.
Soon after the US citizens drove into the border city of Matamoros, Mexico (pictured above), on Friday, they were fired upon by unidentified gunmen, a release from the FBI in San Antonio said. The agency did not identify the victims.
"All four Americans were placed in a vehicle and taken from the scene by armed men," the release said.
The US citizens were driving a white minivan with North Carolina license plates, according to the FBI.
The FBI is seeking the public's help in locating the Americans and identifying those responsible for the kidnapping. The agency announced a reward of $50,000 for the return of the victims and the arrest of those involved.
The FBI said it is cooperating with other federal partners and Mexican law enforcement agencies to investigate the kidnapping.
CNN has reached out to the FBI for further information on the victims and has also sought comment from the government of Tamaulipas, the Tamaulipas Secretary of Public Security's office and the Mexican Attorney General's Office.
The US State Department has issued a "Level 4: Do Not Travel" advisory for US citizens thinking of going to Tamaulipas, citing 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," the State Department advisory says.