MEXICO CITY - A woman sits on the ground next to a white Chrysler Pacifica minivan. It's wedged against a red Chevrolet. The driver's side window appears to have been punctured by a bullet; the tires are deflated. Close by, three other individuals lie immobile on the road.

Then armed men wearing protective vests force the woman to the back of a white pickup. The three others are dragged to the truck, trailing what appears to be blood on the ground. A fifth person, apparently injured, lies on a sidewalk.

Video and photographs verified by The Washington Post capture a chaotic scene at an intersection in the border city of Matamoros, Mexico, just three blocks from the United States, where officials from both countries say four U.S. citizens were fired on and abducted Friday.

The four remained missing Monday; the FBI offered a $50,000 reward for their safe return and information leading to the arrests of those responsible.

The Americans came under fire shortly after they crossed the border Friday into the city of Matamoros, across from Brownsville, Texas, the FBI said in a statement Sunday. The Americans were traveling in a white minivan with North Carolina plates.

"All four Americans were placed in a vehicle and taken from the scene by armed men," the bureau said.

Officials do not believe the victims were targeted before the encounter. There was no evidence they were linked to organized crime in Mexico, U.S. officials said; none of the four have criminal records.

Mexican President Andrés Manuel López Obrador said the Americans had "crossed the border to buy medicine in Mexico" when they were caught in a crossfire "between groups." Ken Salazar, the U.S. ambassador to Mexico, said an "innocent Mexican citizen" was killed.

Oliver Rich, the special agent in charge of the FBI's San Antonio Division, said the bureau was seeking assistance from the public in identifying the kidnappers. The FBI did not release names of the victims. The bureau is investigating the kidnapping alongside Mexican law enforcement agencies.

The San Antonio Division declined to provide more details Monday. The State Department and Mexican police did not respond to requests for further comment.

The White House said that President Joe Biden had been briefed and that it was "closely following the assault and kidnapping" of the Americans.

"These sorts of attacks are unacceptable," White House spokeswoman Karine Jean-Pierre said in a news briefing. "We stand ready to provide all appropriate consular assistance." She said U.S. law enforcement and the State and Homeland Security departments would "continue to coordinate with Mexico and push them to bring those responsible to justice."

Matamoros, home to 580,000 people, is the second-largest city in the northeastern state of Tamaulipas, across from Texas's southern tip. Tamaulipas is one of six Mexican states to which the State Department advises Americans against traveling, citing the risk of 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 says. Heavily armed members of criminal groups often patrol border regions in the state.

On the day of the kidnapping, the U.S. Consulate in Matamoros said it had received police reports of a deadly shooting in the city and ordered U.S. government officials to avoid the area in the vicinity of Calle Primera and Lauro Villar. There was no immediate indication that the incident was connected to the kidnapping.

Tamaulipas is among the most dangerous states in Mexico, largely because of violent conflict between armed groups warring for territory. Some of those groups in recent years have used kidnapping as a revenue stream, at times abducting migrants waiting along the border.

But security in Matamoros has improved in recent years, with fewer high-profile attacks like the one that preceded Friday's kidnapping. Many Americans who live across the border in Brownsville walk or drive to Matamoros for lunch or to see a doctor. In January, Texas Monthly published a list of the city's best taquerias.

Matamoros is firmly in the hands of the Gulf Cartel, but fractures within that group have led to waves of violence elsewhere in Tamaulipas state. Analysts have expressed concern that if similar fissures emerge in Matamoros, the city's relative peace could be disturbed.