Many migrants from Central America board the train in the hope of a new life in the US, but hundreds of them never make it through the treacherous trek in Mexico.
In the most recent case, a group of at least 40 passengers were tied up and they "disappeared".
Central American authorities have long urged Mexico to ramp up security along these human smuggling routes.
Now Honduras, Guatemala and el Salvador are demanding that Mexican authorities investigate last week's abductions.
