IXTEPEC, Mexico—Hundreds of migrants hoping to reach the United States boarded a freight train in southern Mexico late on Thursday, frustrated by efforts to slow their progress by the Mexican government, which is under pressure from U.S. President Donald Trump.

Central American migrants, moving in a caravan through Juchitan, Oaxaca are pictured atop a train known as "The Beast" while continuing their journey toward the United States, in Mexico on April 26, 2019. Jose Cortes/Reuters
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