WASHINGTON (AP) — The Latest on the Trump administrations plan to send troops to the U.S.-Mexico border (all times local):

10:42 a.m.

A U.S. official says Defense Secretary Jim Mattis has directed the military to work out details of a troop deployment to the southern border that could number 800 or more.

Mattis, who is traveling in the Middle East, signed paperwork accepting a written request for military assistance from the Department of Homeland Security. He also authorized the Pentagon’s military staff to determine the size, composition and estimated cost of the deployment.

The intent is to have the troops in position to assist the Border Patrol by Oct. 31, the official said. The official spoke on condition of anonymity to describe aspects of planning that has not yet been completed or announced.

The troops are expected to provide a variety of air and land transportation assistance, as well as engineering help and other specialized forms of support like medical care.

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12:19 a.m.

The Trump administration is planning to dispatch 800 or more active duty troops to the southern border at the direction of a president who has sought to transform fears about immigration into electoral gains in the midterms as a caravan of thousands of migrants makes its way through Mexico.

Defense Secretary Jim Mattis is expected to sign an order sending the troops to the border, bolstering National Guard forces already there. The action comes as President Donald Trump has spent recent days calling attention to the caravan of Central Americans slowly making their way by foot into southern Mexico, but still more than 1,000 miles (1609 kilometers) from U.S. soil.

Trump has been eager to make it a top issue in the midterm elections, as he did in 2016.