Hundreds more Central American migrants have crossed into Mexico from Guatemala, and a group of about 1,000 has started walking en mass to the north.
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State and local police accompanied the migrants Wednesday as they walked along a highway leading from the border to the first major city in Mexico, Tapachula.
In recent months Mexico has used raids and roadside checkpoints to discourage highway marches such as the massive migrant caravans that occurred in 2018 and early 2019.
But no such dissuasive force was seen Wednesday.
The migrants say they aim to reach the U.S. border, where many plan to request asylum.
U.S. President Donald Trump has threatened to slap tariffs on Mexican imports unless Mexico does more to stop the passage of migrants through its territory.