AUSTIN — Federal immigration officials are extending the tenure of the 1,000 National Guard troops Gov. Greg Abbott deployed to the southern border to help slow an influx of migrants.

In June, Abbott said the federal government would pay 100% of the costs for what would be a "short-term mission" to last through Sept. 30. In mid-August, the U.S. Department of Homeland Security requested an extension through Nov. 30.

The Pentagon, which is paying for the state's deployment, has approved an extension through Nov. 15, spokesman Christian Mitchell said. But it is still unclear how much the mission has cost American taxpayers.

Abbott in June cited an "escalating crisis" as more than 144,000 migrants crossed the country's southwestern border the previous month, leading to overcrowding in federal holding facilities that resulted in allegations of child neglect and poor treatment by immigrants rights lawyers.

Though the number of apprehensions at the Mexican border has fallen significantly since the peak in May to about 64,000 in August, that's still nearly 20,000 more than the same month last year.

The troops are under Abbott's command. The governor's office and the Texas Military Department have given few details on their duties and fought a public records request for that information by The Dallas Morning News, claiming the release of the information could aid terrorists and other criminals.

The 1,000 troops at the border are tasked with "supplemental staffing and support" at immigrant holding facilities in Donna and Tornillo, near El Paso. The troops deployed to those facilities did not arrive until early August, more than a month after Abbott's announcement.

Others are providing "point of entry enforcement support" at designated points of entry and airports to improve border security and the flow of commercial traffic.