They joined a smaller group of about 80 migrants who reached the border city on Sunday. "The trip was so tiring".
As far as costs of the deployment, Mattis said he would update reporters as they become known.
" 'CBP has been and will continue to prepare for the potential arrival of thousands of people migrating in a caravan heading towards the border of the United States, ' said Pete Flores, Director of Field Operations in San Diego".
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With a small group of Central American caravan members already in Tijuana, thousands of others continued their push to the US border on Monday, as shelters, church leaders and government authorities in Baja California braced for their arrival.
Francisco Rueda Gomez, Baja California's secretary-general, said that the arrival of the large group could be days or weeks away. Space in shelters operated by church and civic groups in Tijuana and Mexicali is limited in the state to 1,600 spaces, he said, and some already are filled to capacity. "But we will make room".
Authorities have been struggling to deal with the first sizeable group of 357 migrants who arrived in the border city of Tijuana, Mexico, aboard nine buses. "These preparations include training exercises, deploying additional CBP personnel, and partnering with the US military to harden our ports of entry and the border area between those legal crossings into the U.S". For all those who apply for asylum, only a small percentage receive it.
Ahead of last Tuesday's midterm elections, President Donald Trump and his administration had ramped up rhetoric against the caravans, with the USA leader vowing to stop what he called an "invasion" at the border. The move was quickly challenged in court. President Donald Trump has said the caravan of migrants amounts to an "invasion". Few trucks passed, and migrants felt stranded. We've had migration for years, and these people just want to get to the US.
Tijuana resident Juan Carlos Ruano wrote on the neighbourhood Facebook page that the migrants were a security concern and called them "homo-deviant invaders". "They wanted to be taken to another state, that can't be done". He was staying at the same tent shelters set up for the first caravan at a sports stadium in Mexico City.