In a case of mistaken identity, four U.S. citizens were attacked and abducted by gunmen in northeastern Mexico on Friday, a U.S. official familiar with the inquiry told CNN.

The Mexican cartel thought the Americans were Haitian drug dealers and targeted them.

Meanwhile, the authorities have found no evidence of any concerning criminal background on the part of the Americans.

The Mexico kidnapping victims had driven to the Mexican border city of Matamoros for medical operations, the official claimed, citing invoices found in the car.

President Andrés Manuel López Obrador of Mexico provided a similar justification.

"The information we have is that they crossed the border to buy medicines in Mexico, there was a confrontation between groups, and they were detained," the president said. "The whole government is working on it."

The occurrence draws attention to the expanding industry of so-called "medical tourism" and the continued violence in several Mexican communities plagued by organized crime, at least since the Mexican Drug War began in 2006.

The unidentified missing Americans arrived in Matamoros Friday in a white minivan with North Carolina license plates, according to the FBI in San Antonio.

Unknown gunmen opened fire on them before they were put in a vehicle and carried away from the site by armed men, as reported by the FBI.

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The Mexico Kidnapping Incident According to Witness

The shooting and kidnapping appeared to have occurred in broad daylight, according to a witness driving through Matamoros and requesting anonymity for fear of reprisal.

The white minivan was struck by another car at a crossroads, followed by gunfire, said the witness. Another vehicle pulled up, and many men with guns jumped out.

"All of a sudden, they (the gunmen) were in front of us," she said. "I entered a state of shock; nobody honked their horn, and nobody moved. Everybody must have been thinking the same thing, 'if we move, they will see us, or they might shoot us.'"

The assailants pushed a woman into the bed of a pickup truck. Another victim was also transferred to the car, according to the witness.

"The other two they dragged across the pavement; we don't know if they were alive or dead," the witness stated.

Minutes afterward, the Mexio authorities showed up.

Rival sections of the Gulf cartel rule Matamoros, and this tableau depicts the constant state of fear that has permeated the city for years, AP reports.

Thousands of Mexicans, including residents of Matamoros, have vanished in the state of Tamaulipas due to the violence.

Mexico Kidnapping Incident Caught on Video

The moment they were abducted has been captured on Twitter, according to CBS News' Christina Ruffini.

A woman was walking alone when a man in a white pickup truck accosted her. Next, the men with the long weapons and the protective vests start hauling people into the car, one by one.

The condition of the Mexico crime victims is unknown, but there is a chance that a few of them were hurt, based on the footage that surfaced online.

An "innocent" Mexican national was killed in the kidnapping, U.S. Ambassador to Mexico Ken Salazar stated in a statement released Monday.

While he could not provide any further information, he said that various U.S. law agencies collaborated with their Mexican colleagues to locate the missing Americans.

The FBI has announced a reward of $50,000 for information leading to the safe return of the victims of the Mexico kidnapping and the perpetrators' capture.

Disputes between rival groups within the Gulf drug cartel have made Matamoros a battleground recently, leading to widespread Mexico crime on Friday and a warning from the U.S. Consulate and police to stay indoors.

The alert also served as a gentle reminder to the American people that the U.S. State Department has issued a "Level 4: Do Not Travel" warning for this region of Mexico.

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Written by: Bert Hoover

WATCH: FBI demands return of four Americans kidnapped in Mexico - From CBS Mornings