A group of Mexicans present in St Peter's Square for the Wednesday audience cheered and waved a Mexican flag at the comments.
Francis has frequently been vocal in his support of Mexico's efforts to help migrants and critical of the United States for blocking migrants at the border.
During a visit to the US-Mexico border in 2016, he criticised then-presidential candidate Donald Trump, suggesting that anyone who wanted to build a wall along the border was "not a Christian".
In April, the pontiff donated 500,000 US dollars to help migrants in Mexico, offering assistance to local projects that provide food, lodging and basic necessities.
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