The U.S. military will be sending 5,000 support troops to the U.S.-Mexico border, the Pentagon announced on Monday.

The exact number could be slightly higher or lower, a Pentagon official told NPR. The official said the deployment is being done to support the Department of Homeland Security and Customs and Border Protection.

The uniformed troops will likely be active-duty Army personnel, with perhaps some members of the Army Reserve and Marines. There are already 2,100 National Guard members deployed to the border.

Because the Posse Comitatus Act prohibits the U.S. military from performing law enforcement activities within the United States, these troops will be in support roles only. They will not have arresting power and won't interact with migrants.

Those deployed will include engineers, planners, military police, pilots, cooks and medical personnel. Among the work the troops will undertake is the building of camps to house CBP personnel along the Mexican border.

The troops will come from Army bases around the country, including Fort Bragg in North Carolina, Fort Riley in Kansas, Fort Campbell in Kentucky, and Joint Base Lewis McCord in Washington. By the end of the week, they'll head to staging bases in California, south Texas and Arizona.

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