A reward of $50,000 (£41,700) has been announced by the FBI for help in saving four US citizens kidnapped in Mexico.
According to the FBI, the four Americans were travelling in a white minivan with North Carolina licence plates when they crossed into Matamoros, Tamaulipas, on Friday.
The unidentified gunmen fired upon the passengers in the vehicle shortly after they entered Mexico in in warring cartel territory.
The armed men then kidnapped the US citizens, who have not yet been identified, and fled the scene, the FBI said.
A release said: "All four Americans were placed in a vehicle and taken from the scene by armed men."
A video allegedly shows gangsters dragging the men into a pickup truck after the two groups exchanged gunfire.
The bureau along with Mexican law enforcement agencies has launched an investigation, led by Oliver Rich, the special agent in charge of the San Antonio Division of the FBI.
The public is urged to contact the FBI San Antonio Division at 210-225-6741 with any information related to the investigation, while tips can also be submitted online at the bureau's TIP website.
Local residents claimed the Americans were committing criminal activity in the area before they were kidnapped, though this hasn't been independently verified and the reason for their visit is currently unknown.
Matamoros is home to warring factions of the Gulf drug cartel.
The shootouts in Matamoros were so bad that the U.S. Consulate issued an alert about the danger Friday.
Tamaulipas state police said people had been killed and injured Friday, but did not say how many.
Matamoros is a city in Mexico's Tamaulipas state, which has a "Level 4: Do Not Travel" warning on the US State Department website.
The severe advisory is due to risks of crime and kidnapping.
The site says: "Organised crime activity – including gun battles, murder, armed robbery, carjacking, kidnapping, forced disappearances, extortion, and sexual assault – is common along the northern border and in Ciudad Victoria.
"Criminal groups target public and private passenger buses, as well as private automobiles travelling through Tamaulipas, often taking passengers and demanding ransom payments.
"Heavily armed members of criminal groups often patrol areas of the state and operate with impunity particularly along the border region from Reynosa to Nuevo Laredo.
"In these areas, local law enforcement has limited capacity to respond to incidents of crime.
"Law enforcement capacity is greater in the tri-city area of Tampico, Ciudad Madero, and Altamira, which has a lower rate of violent criminal activity compared to the rest of the state."
