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The Department of Homeland Security has sent the Defense Department a new request to build hundreds more miles of border wall, according to a senior defense official.

The request for funding, or RFA, which was made Wednesday, asks the Defense Department to use money earmarked for counternarcotics to build the wall along six sectors of the U.S.-Mexico border — about 270 miles across several states.

The official wouldn't say how much the construction would cost, saying that it was still being assessed and that it was not even certain that the Pentagon would be able to fulfill the entire request.

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Although there's no price tag yet, the Pentagon obligated $2.4 billion of counternarcotics funds for 129 miles of wall last year.

The Defense Department is beginning an assessment of the RFA now — including examining the legality of the request, the feasibility of construction, the impact on military readiness and the source of the funding.

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Defense Secretary Mark Esper should get a recommendation on each of the four issues in about two weeks and then decide whether the Pentagon will fulfill the request, the official said.

If the RFA is approved, the money would come from counternarcotics, but that budget most likely won't have enough funds to cover the request. As a result, funding would likely be transferred from other accounts, as it was last year.

The Department of Homeland Security didn't get enough money in its budget to cover the border construction this year, prompting the request to the Pentagon.

"I think everybody would prefer that DHS get funded to do the border barrier construction," the official said.

About 104 miles of wall have been built to date, and almost 1½ more miles are being constructed every day, the official said. The goal is to finish 400 to 500 miles by the end of the year.

The official expects construction to accelerate, surpassing the 1½ miles a day. The United States has about 5,100 National Guard and active duty troops at the border.