There are around 3,000 active-duty troops serving at the southern border in response to what the White House has declared is a national emergency.

A contingent of the forces deployed to the US-Mexico border will spend the next month painting the border wall in C alexico, California to "improve the aesthetic appearance," a DHS email notifying Congress of the plans explained.

Lawmakers have condemned the plan, calling it a waste of taxpayer dollars and misuse of US military manpower.

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US troops deployed to the southern border amid a national emergency will be spending a month painting President Donald Trump's border wall, an email sent by the Department of Homeland Security to Congress revealed, a congressional aide told INSIDER.

Senator Dick Durbin, a Democrat from Illinois, confirmed the plans on Twitter Thursday, revealing that "the primary purpose is to improve the aesthetic appearance." He condemned this as a waste of taxpayer dollars, adding, "Our military has more important work to do than making Trump's wall beautiful."

"These are soldiers, they are not painters," Rep. Joaquin Castro, a Texas Democrat, told CBS News.

Read more: US troops stationed at the border will spend 30 days painting Trump's steel barrier

Active-duty US military were deployed by the thousands to the US-Mexico border starting last October in response to the arrival of migrant caravans from Central America. The president has repeatedly referred to these caravans as invaders, even at times suggesting that the military should use force.

A U.S. Customs and Border Protection vehicle sits near the wall as President Donald Trump visits a new section of the border wall with Mexico in Calexico, Calif., Friday April 5, 2019. AP Photo/Jacquelyn Martin

US troops have been constructing barriers and running razor wire, as well as providing support to DHS operations on the border. DHS argues that painting the fence has "operational benefits" beyond pure aesthetics.

Trump reportedly instructed engineers to paint the wall's bollards black to absorb heat and make them difficult to climb.

Read more: Trump reportedly wants to paint his border wall black so it can absorb heat and get too hot for people to climb

The federal agency noted that the recently-painted barriers in Tuscon, Arizona had helped Border Patrol beat the "camouflaging tactics of illegal border crossers." DHS also noted that "individuals appeared to have greater difficulty" climbing the newly-painted walls in Nogales, Arizona.

US troops are expected to paint a section of the wall in Calexico, California, and the project is expected to last "approximately 30 days."

President Trump declared a national emergency on February 15 after a showdown with Congress for border funding, arguing that "the current situation at the southern border presents a border security and humanitarian crisis that threatens core national security interests."

There are currently 3,000 active-duy US troops on the southern border serving alongside roughly 2,000 National Guard units.