MEXICO CITY -- The remnants of a caravan of Central American migrants are protesting in northern Mexico as they once again draw angry tweets from U.S. President Donald Trump.

The mainly Central American migrants are demanding better treatment and many are planning to request asylum, either in the United States or Mexico.

The approximately 500 migrants arrived in the northern city of Hermosillo aboard trains over the weekend.

Organizer Irineo Mujica has said the migrants plan to arrive in Tijuana later this week. Trump tweeted Monday that “I have instructed the Secretary of Homeland Security not to let these large Caravans of people into our Country.”

Homeland Security Secretary Kirstjen Nielsen said Monday that “If members of the 'caravan' enter the country illegally, they will be referred for prosecution for illegal entry.”

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