The request for bus travel for all also indicates an increased sense of urgency amongst the caravan's members to make it to the USA border - despite thousands of American troops awaiting them there and a steady drumbeat of warnings from President Trump and US officials to turn around.
Migrants -mostly Hondurans- taking part in a caravan heading to the U.S., hold Honduran and Mexican national flags as they walk along the road on their way to Matias Romero, at La Ventosa, Oaxaca State, Mexico, on November 1, 2018.
Trump made the announcement after a wave of falsehoods, many of them racially charged, about what he again called an "invasion" of Central American migrants and asylum seekers now traveling toward the US border.
Trump has said he's willing to send as many as 15,000 troops to the USA border ahead of its potential arrival. So their role would largely be limited to activities such as providing helicopter support for border missions, installing concrete barriers and vehicle maintenance, rather than detaining migrants.
"The support that we provide to the secretary for Homeland Security is practical support based on the request from the commissioner of Customs and Border Police", he replied. The caravan is still more than 1,100km away and is not expected to make it to the U.S. border for weeks.
With his eyes squarely on Tuesday's contests, Trump has rushed a series of immigration declarations, promises and actions as he tries to mobilize supporters to retain Republican control of Congress.
The leading caravan is still about 900 miles from the closest entry point into the US - but their intended route remains a mystery.
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"Trump says, as always without any evidence, that asylum seekers are given phony statements to read when they get to the border". He also tweeted: "We will NOT let these Caravans, which are also made up of some very bad thugs and gang members, into the U.S. Our Border is sacred, must come in legally".
Just 24 hours later, Trump thrust new uncertainty into the picture, catching the Pentagon by surprise.
The ostensible reason for the military operation dubbed "Operation Faithful Patriot" has been to free up the Border Patrol to carry out repressive measures against the caravan of immigrants, mostly women and children fleeing horrific violence and poverty in Central America. Many have said they plan to apply for asylum at an official port of entry, as other caravans have done in the past.
Of the caravan he said: 'Nobody's coming in.
The first caravan, which has dwindled and now numbers some 4,000 people, according to an aide group called Pueblos sin Fronteras, arrived Tuesday in the town of Juchitan, in Oaxaca. "Previous protests in support of immigration caravans or enforcement of immigration law have occurred throughout the US". And this week he is asserting he could act by executive order to unilaterally end birthright citizenship for the children of non-U.S. citizens.
The figures Trump suggested are on par with the number of troops now stationed in Afghanistan, 14,000, and more than twice as many as those stationed in Iraq, 5,200.
The U.S. military is sending military police, engineers, helicopter teams, command and military planning units, medical teams, transportation and logistics teams to the border.