The number of U.S. troops deploying to the U.S. southern border has increased to more than 8,000, two U.S. defense officials told VOA Friday.
President Donald Trump ordered the troops to keep a caravan of asylum-seeking migrants from Central America from entering the U.S.
The officials described the active duty troops as “deployed, deploying, or identified to deploy” to help with border security in response to a request for help from the Department of Homeland Security.
"We just have a capacity issue, " Homeland Security Secretary Kirstjen Nielsen said in explaining the need for the troops. "What we've asked the [Department of Defense] to do is to support us."
Another 2,100 National Guard troops are already deployed along the southern border. Altogether, there are now more U.S. troops assisting border patrol agents than there are fighting terror groups in Iraq and Syria.
Speaking to reporters at the White House before leaving for another campaign-style rally in Huntington, West Virginia, to drum up support for Republican Senate contender Patrick Morrisey, Trump said Friday that troops would not shoot at migrants who had thrown rocks at them.
"I didn't say shoot. I didn't say shoot. But they do that with us, they're going to be arrested for a long time," Trump said.
A day earlier in his speech on immigration, Trump suggested he had directed the military to shoot migrants who throw rocks at U.S. border authorities. Experts and retired military officials have pointed out that such a directive would be unlawful because it violates U.S. military conventions.
Meanwhile, a group of the migrants traveling to the U.S. to seek asylum have filed a lawsuit against Trump.
Attorneys for six Honduran migrants filed the class-action lawsuit Thursday in U.S. District Court in Washington, alleging Trump violated their due process rights under the Fifth Amendment of the U.S. Constitution.
The suit cites a ruling by the late Supreme Court Justice Antonin Scalia, who wrote, "It is well established that the Fifth Amendment entitles aliens to due process of law in a deportation proceeding."
Trump has been using the migrant caravan to rally his Republican base before next week's midterm elections, declaring on several occasions its approach toward the U.S. constituted a "national emergency."
Trump again raised fears Thursday about undocumented immigrants and promised an executive order "sometime next week" that would severely restrict asylum-seekers.
At a political rally Thursday night in Columbia, Mo., Trump said several times that he also intended to end birthright citizenship. The 14th Amendment to the Constitution guarantees U.S. citizenship to anyone born in the United States. The president said at the rally that he was against "birth tourism," in which pregnant foreign women travel to the U.S. to give birth so that the babies can automatically be U.S. citizens.
Trump said he could change the 14th Amendment with an executive order, but many legal analysts disagree, maintaining the Constitution cannot be changed by executive order alone.
The president added that migrants attempting to seek asylum must make their requests at legal points of entry, and said he wanted to increase the detention of asylum-seekers.
As more troops arrive at the Texas-Mexico border, some military experts argue that sending troops to the border is a distraction from the military's top priority of being more "lethal" at war, as Defense Secretary James Mattis put it.
Former Department of Homeland Secretary Tom Ridge decried Trump's use of the U.S. military at the border, telling VOA, "They're not trained to deal potentially with a group of unarmed immigrants."
Retired Marine colonel and and current vice president at the Bipartisan Policy Center David Lapan said deploying troops at the border "doesn't make any sense." He added, "This caravan, this group of poor people, including a lot of women and children, doesn't pose a threat, not a national security threat."
The migrants are still more than 1,000 kilometers from the U.S., a distance that will likely take at least several weeks for them to walk.
WATCH: Trump: Migrant Caravan Should Turn Back
VOA Pentagon correspondent Carla Babb contributed to this report.