Armed criminals abducted 31 migrants traveling by bus in Tamaulipas on Saturday, according to authorities in the northern border state.

Five of the victims were located, but the other 26 remain missing.

Tamaulipas security official Jorge Cuéllar Montoya said in an interview on Monday that a bus driver reported the abduction of 31 of 36 passengers on the Reynosa-Matamoros highway.

A bus operated by Grupo Senda, a Monterrey-based bus company, was intercepted by armed men in five pick-up trucks, Cuéllar said.

The bus was traveling to Matamoros, Tamaulipas, from Monterrey when the incident occurred, he said.

“According to the driver’s report, … 31 passengers of different nationalities were taken by these five trucks,” Cuéllar said.

The migrants are reportedly from Venezuela, Honduras and Colombia. According to a Reforma newspaper report, they were traveling to Matamoros to attend appointments with U.S. immigration authorities.

Cuéllar said that state and federal security forces had been searching for the missing migrants, but hadn’t located any of them.

However, the Tamaulipas government said Monday night that the National Guard found five Venezuelans including two children in a vehicle traveling on the Monterrey-Matamoros highway in Reynosa, a border city opposite McAllen, Texas.

In a post to Facebook, the government said that the vehicle performed “evasive maneuvers between traffic” before coming to a halt. Two men subsequently fled on foot.

The Venezuelan migrants told authorities they were kidnapped while traveling on a Senda bus.

The government said that the five migrants were taken to National Immigration Institute offices. The vehicle in which they were being transported was seized and will be turned over to the Tamaulipas Attorney General’s Office, according to the social media post. According to a report from El País newspaper, Cuéllar indicated the five migrants were a “separate case” from the Saturday mass abduction, but provided no further details.

The abduction of the migrants on Saturday came after weeks of warnings from migrant advocates of an increase in kidnappings in the border region of Tamaulipas, according to Reforma.

The newspaper noted that Cuéllar didn’t explain “how the criminals were able to commit this mass kidnapping with impunity on one of the state’s most important highways and during holiday season when there is a heavy flow of travelers and security has supposedly been strengthened with [the presence of] police and the military.”

Migrants are frequently targeted by criminal groups as they travel through Mexico toward the northern border. Many have been forcibly recruited by cartels, while others have been killed.

Forty-nine migrants were kidnapped while traveling through San Luis Potosí by bus in May last year. They were subsequently rescued.

With reports from El Universal, Reforma, El País and López-Dóriga Digital