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(CNN) —  

President Donald Trump claimed that up to 15,000 US troops could be sent to the border to deal with the group of approximately 3,500 migrants heading toward the US through Mexico.

The migrants, who are more than 800 miles away from the US, are weeks away from arriving at the border, where many reportedly plan to follow legal procedures and seek asylum.

“As far as the caravan is concerned our military is out, we have about 5,000-8 (thousand), we’ll go up to anywhere between 10 (thousand) and 15,000 military personnel on top of border patrol, ICE and everybody else on the border,” Trump told reporters Wednesday.

The Pentagon has already announced 5,200 active duty troops are being sent to the border and has identified an additional 2,000 that could go. There are currently 2,100 National Guardsmen on duty at the border and an additional 2,000 could be called upon to go if needed.

Shortly after Trump spoke, the Pentagon released a statement saying “The number of troops deployed will change each day as military forces flow into the operating area, but the initial estimate is that the DOD will have more than 7,000 troops supporting DHS across California, Arizona and Texas.”

Senior military officers have defended the deployment on national security grounds. The mission – dubbed Operation Faithful Patriot – will “provide a range of assistance, including planning, engineering, transportation, logistics and medical support to the US Customs and Border Protection,” according to the Pentagon.

But Trump has painted a different picture with his rhetoric, casting the deployment as a necessary intervention to stop potentially dangerous individuals from entering the country.

“Trump is painting a word picture for his political base of troops arrayed along the border to hurl back invaders, when what he is really sending are mechanics, construction workers, planners, supply clerks and pilots who will be planning, building, supplying, flying and repairing,” said CNN military analyst John Kirby.

Trump doubled down on the threat posed by the migrants earlier Wednesday and said he’d be sending “many more” troops to the border.

“Our military is being mobilized at the Southern Border,” the President tweeted. “Many more troops coming. 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. TURN AROUND!”

Later, Trump added that he is thinking “very seriously” and “immediately” of stopping aid to countries where people in the group of migrants are coming from.

“Nobody’s coming in. We’re not allowing people to come in,” Trump said. “If you look at what happened in Mexico two days ago with the roughness of these people in the second caravan that’s been forming, and also frankly in the first caravan, and now they have one forming in El Salvador. … We are thinking very seriously, immediately stopping aid to those countries because frankly, they’re doing nothing for the American people.”

“Immigration is a very, very big and very dangerous – a really dangerous topic and we’re not gonna allow people to come into our country that don’t have the well being of our country in mind,” he added before insisting that he is not “fear mongering.”

Yet Trump’s announcement Wednesday that “up to 15,000” troops will be sent to the border has only fueled scrutiny from critics who have condemned the deployment as a political stunt by a President eager to fire up his political base just days away from the midterm elections.

Many have pointed out that Trump’s latest figure exceeds the number of US troops currently serving in Afghanistan, which stands at approximately 14,000.

Defense Secretary James Mattis pushed back against that assertion by critics Wednesday, telling reporters, “We don’t do stunts.”

While the sheer size of the deployment has made headlines, Kirby cautioned that troop numbers are “mission specific” and should not be used to compare the US military’s presence in different parts of the world.

“It’s not about the footprint. It’s about the mission. And sometimes enabling missions — especially if that’s all you’re going to do — require a significant footprint,” he said, pointing out that US troops deployed to the border will serve as “enablers” rather than “trigger-pullers.”

Another concern that has been raised is the unknown cost to taxpayers, given that much smaller deployments of National Guard to the border have cost hundreds of millions of dollars.

Congressional sources told CNN on Wednesday that relevant lawmakers have not yet received cost data from the Pentagon. Pentagon spokesperson Christopher Sherwood told CNN Tuesday that details related to the final price tag are still being worked out.

CNN’s Ryan Browne contributed to this report.