Mexican authorities have increased immigration enforcement along well-travelled routes in southern Mexico, 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 US to reduce the surge of mostly Central American migrants through its territory.
Mexico plans to deploy 6,000 National Guard troops by Tuesday to its southern border with Guatemala.
In the Gulf coast state of Veracruz, the National Migration Institute said 791 people were taken to a migration facility on Saturday and the 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.
Military police wearing National Guard armbands were also patrolling Sunday along the Suchiate River that separates Mexico from Guatemala.
In prior days, migrants were seen being ferried across the river by raft without interference from immigration or other Mexican officials.
Outside Comitan on Sunday, some roadblocks and checkpoints were manned by multiple soldiers and police identifying as National Guard.
The Mexican National Guard is a new security force created by President Andres Manuel Lopez Obrador, who took office 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.
Australian Associated Press
