Mexican immigration authorities say 424 migrants from African countries arrived at the southern state of Chiapas over two days last week.

The National Immigration Institute said Tuesday that it has issued them 20-day transit visas that will allow the migrants to reach the U.S.-Mexico border, where they plan to request asylum.

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Immigration support staff in Tijuana has been aiding migrants from the Congo, Somalia and Ghana to arrive at the U.S. port of entry at San Isidro.