The Pentagon has authorised the transfer of $1 billion (£758 million) to build a new wall along the US-Mexico border.
In a significant victory for US president Donald Trump, the money will be distributed to army engineers to plan and build a 57-mile stretch of “pedestrian fencing”, roads and lighting along the border.
Building the wall was a major promise of Mr Trump’s presidential election campaign, but he has met opposition to the plan from Congress.
He declared a national emergency last month in an effort to fund the controversial wall without congressional approval.
Last week, the Pentagon gave Congress a list that included $12.8 billion (£9.7 billion) of construction projects for which it said funds could be redirected for construction along the border.
Acting secretary of defence Patrick Shanahan said in a memo to secretary of homeland security Kirstjen Nielsen that the Department of Defence had the authority to support counter-narcotics activities near international boundaries.
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Mr Shanahan authorised the US Army Corps of Engineers to begin planning and executing the project that would involve building 57 miles of 18ft—high fencing, constructing and improving roads, and installing lighting within the Yuma and El Paso sections of the border.
Mr Trump says the situation at the border is a “crisis” and says the wall is needed to prevent criminals getting into the US, but critics say he has concocted the border emergency.
Democrats have complained that the Pentagon did not seek permission from relevant committees before telling Congress about the funding.
Building the wall was one of Mr Trump’s most oft-repeated campaign promises, though he claimed the money would come from Mexico, not American taxpayers.
Mr Trump’s emergency declaration drew unanimous opposition from congressional Democrats and opposition from some Republicans, especially in the Senate, where politicians objected that he was abusing presidential powers.
It has been a good week for Mr Trump after Attorney General William Barr said special counsel Robert Mueller had ended his two-year investigation without evidence of collusion by his 2016 campaign with the Russian government.
Democrats were hoping to use the border emergency battle in upcoming campaigns, both to symbolise Mr Trump’s harsh immigration stance and claim he was hurting congressional districts around the country.
Last week, the Pentagon sent politicians a list of hundreds of military construction projects that might be cut to pay for barrier work.
Though the list was tentative, Democrats were asserting that Republican politicians were endangering local bases to pay for the wall.