US President Donald Trump's administration may send up to 1000 active-duty troops to the US-Mexico border, officials say, as Trump hammers away at the issue of illegal immigration two weeks before congressional elections.
Trump's threat was sparked by the advance of a caravan of Central American migrants trekking through Mexico, headed toward the United States.
"I am bringing out the military for this National Emergency. They will be stopped!" Trump wrote on Twitter.
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But the migrants appeared undeterred on Thursday night as several thousand of them bedded down more than 1600km from the US border, in the town of Pijijiapan in Mexico's southern Chiapas state.
"Whatever Trump may say, he's not going to hold us back," said Denis Omar Contreras, a caravan organiser from Honduras, who plans to help lead the group to northern Mexico.
Many said the fear of returning to a violent homeland loomed larger than the president's threats.
"We've come fleeing our country. If we return to Honduras, the gangs will probably kill us," he said.
Trump and his fellow Republicans have sought to make the caravan and immigration into major issues before the November 6 elections, in which Republicans are battling to keep control of Congress.
Trump, who has maintained a hard line on immigration since taking office last year, is considering a plan to ban entry of migrants at the southern border and deny them asylum, according to media reports.
A White House official said "a wide range of administrative, legal and legislative options" were being considered but that no decisions had been made.
US Homeland Security Secretary Kirstjen Nielsen said in an interview with Fox News Channel her department had asked the Pentagon for help to bolster its capabilities as it polices the border, including asking for "some air support ... some logistics, planning, vehicle barriers, engineering".
The request could require deploying between 800 and 1000 active-duty troops, two US officials said, speaking on condition of anonymity.
More than 1000 people arrived in Guatemala on Monday, part of a second caravan, but have since divided into smaller groups.
The larger caravan is now in southern Mexico and left Honduras nearly two weeks ago.
It numbered more than 5000 when it settled in the town of Mapastepec on Wednesday night, a local official said.
