A group of migrants, including children, used an improvised rope to try to scale fencing installed on the beach between Tijuana and San Diego, California - but were forced back with tear gas, which agents had not deployed since January 1.
An AFP journalist witnessed only one migrant cross the border, where he was immediately detained.
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It marked the third time in a week that a group of Central Americans had tried to cross the border to ask for asylum on the grounds their lives were threatened by violence at home.
On the first occasion, a week ago, around 50 people made it across, with about 10 more crossing on Tuesday. All were detained by authorities.
"Someone brought them here, they train them because they know that upon crossing they must ask for asylum and that way they won't be deported and they have to be processed according to US laws," said one Tijuana police officer, who requested anonymity because he was not authorised to speak.
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Last November, hundreds of Central Americans that arrived from Honduras as part of a large caravan tried to cross en masse - but only a few succeeded as the crowd was met with tear gas.
In recent months, thousands of Central Americans have arrived in Mexico in several caravans in the hope of finding a better life in the United States.
US President Donald Trump has branded such migrants a threat to national security, demanding billions of dollars from Congress to build a wall on the southern US border.
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