For the second time, the Pentagon denied a request on Monday by Washington, D.C., Mayor Muriel Bowser to activate the National Guard to assist with thousands of migrants who have been arriving in the nation's capital in recent months.

Bowser first asked for National Guard help last month, but it was rejected by the Pentagon on Aug. 4. She then sent another letter on Aug. 11, requesting that 150 National Guard troops be deployed to "help prevent a prolonged humanitarian crisis in our nation's capital resulting from the daily arrival of migrants."

Defense Department executive secretary Kelly Bulliner Holly wrote in a letter to Bowser on Monday that the D.C. National Guard is not trained to assist migrants and activation would lead to "diminished readiness" for the troops.

"The DCNG has no specific experience in or training for this kind of mission or unique skills for providing facility management, feeding, sanitation or ground support," Holly wrote in the letter, which was reviewed by Fox News.

"Approval of this request would also result in a substantial readiness impact to the DCNG," Holly continued. "Devoting the personnel or the facility for such an extended mission would force the cancellation or disruption of military training."

About 7,000 migrants have been bused from Texas to Washington, D.C., since April and another 900 have arrived in New York City, according to Gov. Greg Abbott's office.

"Before we began busing migrants to New York, it was just Texas and Arizona that bore the brunt of all the chaos and problems that come with it," Abbott said Friday. "Now, the rest of America can understand exactly what is going on."

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Bowser called the busing of migrants on Monday a "politically motivated stunt."

"We struggle with a broken immigration system in our country, and we know that cities alone cannot fix it," Bowser tweeted. "We will continue working with federal partners and local NGOs on the best way to set up systems that allow us to manage an ongoing humanitarian crisis."

Texas launched Operation Lone Star to deal with the influx of migrants across the southern border in March 2021.

Since then, Texas law enforcement officials have apprehended nearly 300,000 migrants and seized 326 million lethal doses of fentanyl, Abbott said.

Migrants Texas Border

A migrant family sits after being processed in Roma, Texas, on May 5, 2022. (Brandon Bell/Getty Images)

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The Pentagon also cited the work of several non-government organizations and civilian groups in assisting with the arrival of migrants.

Bowser's office did not immediately respond to a request for comment on Monday.