COMTIAN, Mexico - Mexican authorities stepped up monitoring of well-traveled routes for migrants in southern Mexico over the weekend, checking identifications, pulling migrants off public transportation and intercepting four trucks packed with nearly 800 migrants.

The National Migration Institute said 1,000 immigration agents had been deployed in the north and south of Mexico. The deployment comes as Mexico faces heightened pressure from the United States to reduce the surge of mostly Central American migrants through its territory. Mexico plans to position 6,000 National Guard troops by Tuesday on its southern border with Guatemala.

The Associated Press saw nearly 10 armed soldiers at a checkpoint near Ciudad Cuauhtemoc, in Chiapas state, wearing black armbands to indicate they are part of the National Guard. The soldiers stopped vehicles while immigration officials checked identification and removed passengers without documents. At another checkpoint just north of Comitan in Chiapas, more than a dozen apparent National Guardsmen drove around back roads in the rain and dark, looking for migrants and human smugglers.

In the Gulf Coast state of Veracruz, the National Migration Institute said 791 people were taken on Saturday to a migration facility and that drivers of the tractor-trailer trucks transporting them were arrested.

Migrants are routinely transported through Mexico in packed semis, sometimes in dangerous conditions without food or water or sufficient fresh air. Government video showed officials breaking the lock on the door of one cargo truck and helping migrants out.

The institute described the detentions and arrests in Veracruz as part of a strategy implemented by its new commissioner, Francisco Garduno. The former prisons director assumed the post on Friday, taking over for a sociologist and academic.

Outside Comitan on Sunday, some roadblocks and checkpoints were manned by multiple soldiers and police identifying as National Guard.

At one, immigration agent Jose Angel Ramirez welcomed the help of the National Guard.

"We don't have a way to stop so many and the traffickers pass everywhere," said Ramirez, who was the only agent on duty at his checkpoint.

Nearby, a dozen National Guard agents stood watch over five Hondurans found traveling without papers.

One of the Hondurans, a farmer named Armando who was traveling with a daughter and nephew, broke into tears while saying he'd be killed if returned to his country. After several hours, the Hondurans were transported to a Mexican detention center for migrants.

The Mexican National Guard is a new security force created by President Andres Manuel Lopez Obrador, who took office on Dec 1. The security force is still taking shape and was originally established with the goal of stemming endemic violence. Last year saw the highest number of murders in at least 20 years in Mexico.

Mexican soldiers have long been authorized to search vehicles for drugs or weapons, explained one of the newly-minted National Guard officers, who declined to give his name. Now, he said, they can detain drivers or others suspected of helping the undocumented move through Mexico.

Comitan locals said that trucks often bypass area checkpoints at night. "We don't know what they have inside," said immigration agent Julio Velasco. Mexican officials have set up additional roadblocks in recent days to cover more territory.

Luis Guillermo Lechuga, who sells vests near one of the checkpoints, was skeptical that the increased security presence will reduce the flow of migrants through Comitan and surrounding areas.

"Everything will be the same," said Lechuga, who expressed a mixture of sympathy and annoyance with the travelers. "Nobody leaves their country without problems."

Associated Press