(NewsNation) — U.S. and Mexican officials are still looking for the four Americans kidnapped last week after crossing into Mexico to buy medicine.

The four had entered the border town of Matamoros, across from Brownsville, Texas, on Friday and were traveling in a white minivan with North Carolina license plates.

The FBI is offering a $50,000 reward for the victims’ return and the arrest of the kidnappers.

Mexican President Andrés Manuel López Obrador said Monday, “There was a confrontation between groups, and they were detained,” without offering details.

President Joe Biden had been informed of the situation, and they are “closely following” the matter and “stand ready to provide all appropriate consular assistance,” White House press secretary Karine Jean-Pierre said Monday.

Jean-Pierre said State and Department of Homeland Security are coordinating with Mexican authorities. She declined to answer other questions, citing privacy concerns.

Photographs from the scene viewed by the AP show a white minivan with the driver’s side window shot out and all of the doors open sitting on the side of the road after apparently colliding with red SUV. Multiple people were lying in the street beside it surrounded by rifle-toting gunmen.

Their positions appeared to correspond with the video posted online that was taken from another angle, which showed them being dragged across the street and loaded into the bed of a white pickup. One person who was sitting up in the street walks under their own power to the pickup. At least one other person appeared to lift his head from the pavement before being dragged to the truck.

Tamaulipas state police said people had been killed and injured Friday, but did not say how many. The state police said that neither police nor the military were involved in Friday’s shootouts.

“There have been two armed incidents between unidentified civilians,” the state police said Friday on social media. “The exact number of the fallen is being corroborated.”

Matamoros was one of the cities listed under the State Department’s do not travel list for being a hotspot for drug and human trafficking, and a site for a violent turf war between two cartels.

Matamoros is largely controlled by rival groups within the Gulf Cartel. Shootouts in the region were so bad on Friday, the U.S. Consulate issued an alert about the danger. Local authorities warned people to shelter in place. It was not immediately clear if or how the kidnappings are connected to the violence Friday.

The leader of the cartel Jose Alfredo Cardenas-Martinez, known as El Contador, or the accountant, was indicted by U.S. officials last year

Victims of violence in Matamoros and other large border cities of Tamaulipas often go uncounted, because the cartels have a history taking bodies of their own with them. Local media often avoid reporting on such incidents out of safety concerns, creating an information vacuum.

The U.S. State Department’s travel warning for Tamaulipas state warns U.S. citizens not to travel there. However, being a border city, U.S. citizens who live in Brownsville or elsewhere in Texas frequently cross to visit family, attend medical appointments or shop. It would also be a crossing point for people traveling deeper into Mexico.

There is some kind of travel advisory in 30 of 32 Mexican states for U.S. citizens. Six of those states have a Level 4 do not travel advisory.

“Violent crime — such as homicide, kidnapping, carjacking, and robbery — is widespread and common in Mexico. The U.S. government has limited ability to provide emergency services to U.S. citizens in many areas of Mexico, as travel by U.S. government employees to certain areas is prohibited or restricted. In many states, local emergency services are limited outside the state capital or major cities,” the advisory reads.