In a statement delivered at the White House Rose Garden, he said "walls work" and that an invasion of drugs, gangs and people is unacceptable.
US President Donald Trump has defended his decision to use emergency powers to fund a wall on the US border with Mexico.
In a statement delivered at the White House Rose Garden, he said "walls work" and that an invasion of drugs, gangs and people is unacceptable.
Senior Democrats have already vowed to challenge the move through the US legal system.
Building the wall was a key promise of Trump's election campaign in 2016.
However Democrats say declaring a state of emergency to secure funding to build it is a "gross abuse of power".
Congress had previously refused to pay for the wall in the national spending bill.
The latest development gives Trump access to billions of dollars for his project.
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