Four American citizens have been abducted by unknown, armed men in Matamoros, Mexico, with a $50,000 reward being offered for their return, according to the FBI.

The incident unfolded Friday afternoon, when four passengers were in a white minivan with North Carolina license plates crossing the Mexico border into Matamoros. Just after crossing, the vehicle was fired upon by multiple gunmen, and the four American citizens were then taken away in another vehicle.

Since the abduction, a “Level 4: Do Not Travel” advisory has been issued for U.S. citizens in the Tamaulipas state. The FBI has asked for the public’s help in identifying the perpetrators and in locating the four Americans.

White House press secretary Kayne Jean-Pierre called the attack “unacceptable” and emphasized that all necessary resources will be utilized to find the victims and bring those responsible to