Trump's tweet came as thousands of Central American migrants continue their caravan trek through Mexico toward the hoped-for - but still far-distant - USA border. "Go back to your Country and if you want, apply for citizenship like millions of others are doing!"
But the migrants appeared undeterred on Thursday night as several thousand of them bedded down more than 1,000 miles (1,610 km) from the USA border, in the town of Pijijiapan in Mexico's southern Chiapas state, after hiking hours from their last stop.
Details of Mr. Trump's plan, including a web of complicated legal issues that will most likely prompt a swift challenge in federal courts, were still being finalized on Thursday, according to the people who described it, all of whom insisted on anonymity to discuss an action that is still under development.
"It's hard, and we know this country is unsafe too, but back in Honduras it's even more risky, they kill for nothing", said Josena Anibal Mejia, 27, as he walked with his daughter.
Trump previously said he would send the military to the border if Mexican authorities failed to stop the caravan, which they have. Most are Hondurans, seeking to escape poverty and violence, and include families with children.
The executive action would reportedly involve Homeland Security and the Justice Department issuing a rule, effective immediately, that limits foreign nationals' rights to seek asylum in the USA if they are a part of a population banned by Trump, sources familiar with the administration's plans told the Chronicle.More news: Son of murdered journalist Khashoggi leaves Saudi Arabia for US
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The news came shortly after President Donald Trump said in a tweet that he was "bringing out the military" to address what he's calling a national emergency at the southern border. Kirstjen Nielsen, the Homeland Security secretary, who has briefed Trump about the caravan as well as data showing a large uptick in the number of apprehensions at the border over the past year, has been leading the effort. "They will not be allowed to stay".
In 2017, the US had 331,700 asylum claims, more than any country in the world, according to the U.N. Refugee Agency.
Those troops are mainly serving in a support role to help free up border patrol officers.
The planned deployment of active-duty troops is in response to a request from the Department of Homeland Security, which manages the Border Patrol. "The president should not be using the military to further a partisan agenda".
The US military is prohibited from carrying out civilian law enforcement on American soil unless specifically authorized by Congress.