The disclosure by United States officials illustrates the tension within the administration over using military resources to fortify the border against illegal immigration, a top election issue for President Donald Trump's base.
Secretary of Defense Jim Mattis is sending up to 5,200 troops to the border to defend it from the onslaught of migrants trying to cross into the country. He said they would not be taking part in law enforcement activities like crowd control.
"They want to throw rocks at our military, our military is going to fight back ... we will consider that a firearm" he had said on Thursday.
Meanwhile, a risk assessment by the Defense Department "found that the caravan did not pose a threat to the United States" and that "the caravan would take about a month and a half to get to the US border", CNBC reported. Captain Bill Speaks, another Pentagon spokesman added, "we have not received a request from DHS to build facilities to house migrant families". "But we're going to arrest those people quickly and for a long time".
Trump's order will ultimately cost up to $220 million, CNBC reported today, citing two senior Defense Department officials. The caravan's numbers have dropped from 7,000 to around 4,000 over the last few weeks, while around 3,000 have applied for asylum in Mexico and others haver returned home.
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Around a fifth of Cameroon's 22 million people are English-speaking - a minority whose presence dates back to the colonial period. Militias, who have been demanding the independence of the two English-speaking regions , have called for a school boycott.
Trump has said he could request a deployment of as many as 15,000 troops to the border in support of U.S. Customs and Border Patrol.
Manning also pointed out that soldiers "do not plan to interact with the protesters or migrant" at the border.
There are roughly 2,700 active-duty troops in Texas, 1,200 in Arizona and 1,100 in California, the Department of Defence revealed Monday.
About "200 unregulated armed militia members [are] now operating along the southwest border", says a planning document for Army commanders leading the 5,200 troops Trump has deployed at the border, according to Newsweek.
There is still no official cost estimate made public for the 45-day mission, but Manning said the Defense Department will "absorb" the costs of the operation.
Manning noted that DHS had requested that active duty troops, rather than reservists - who usually partake in operations on U.S. soil - for this operation.