The Department of Defense has awarded nearly $1 billion in contracts to two companies for construction related to a wall along the southern border, the first such contracts to be awarded since President Trump declared a national emergency.

According to a notice on the Pentagon's website, the Army Corps of Engineers awarded a $789 million contract to the company SLSCO Ltd., from Galveston, Texas, for "border replacement wall construction" in Santa Teresa, New Mexico. Barnard Construction Co. Inc., of Bozeman, Montana, was awarded a contract worth $187 million for "design-bid-build construction project for primary pedestrian wall replacement" in Yuma, Arizona.

Six companies submitted bids for the first contract, with three received for the second. Both projects are expected to be completed by fall of 2020.

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Mr. Trump visited the border and toured construction projects along the border last week. Lt. Gen. Todd Semonite, the head of the Army Corps of Engineers, predicted that by "around December of 2020, the total amount of money that we will have put in the ground in the last couple of years will be about 450 miles. That's probably about $8 billion, in total about 33 different projects."

The funding for the contracts announced Tuesday comes from $1 billion the Pentagon reprogrammed from counter-narcotics programs, which the Pentagon can accomplish without congressional approval or a national emergency declaration. The move has drawn blowback from members of Congress, with lawmakers saying it violates a longstanding understanding not to reprogram funds without congressional sign-off.

In February, Congress tried to block Mr. Trump's declaration, with 12 Republicans joining all Democrats in the Senate in a rebuke to the president. However, the president vetoed the joint resolution blocking the national emergency, and the House did not have enough votes to override a veto.

Mr. Trump has embarked on a purge of top officials at the Department of Homeland Security (DHS) in recent days, with Secretary Kirstjen Nielsen, the head of the Secret Service and other top DHS officials all leaving the administration.

The number of migrants apprehended along the border spiked to more than 92,000 in March, officials from Customs and Border Protections said Tuesday.

David Martin contributed reporting.