Mexican rights activists say they have reports of three cases in which private railroad guards have killed migrants trying to ride freight trains to the U.S. border.

Leticia Gutierrez of the Scalabrinian religious order says the organization also has evidence of five migrants being killed by state or local police in recent months.

Central American migrants used to crowd north-bound freight trains until Mexico cracked down in 2014, sending police and migration agents to raid the trains.

But activists said Wednesday that armed guards from a shadowy company based in Mexico state pull migrants from trains, beating them and shooting at them with shotguns.

At least one of the main railway lines in Mexico denied using such guards, and said its own employees simply report migrants to appropriate authorities.