(BBC News) Four companies have been chosen to build prototypes for Donald Trump's planned border wall, US Customs and Border Protection (CBP) said.
The four concrete prototypes will be 30ft (9m) long and up to 30ft tall, and will be built in the coming months.
Officials will then spend up to two months testing the walls for tampering and penetration resistance using small hand tools, CBP said.
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The four contracts are worth up to $500,000 (£387,000) each.
A continuous wall across the entire southern US border was a key promise in President Trump's election campaign.