Trump has promised to build a wall along the US-Mexican border. This map shows where fences are already in place.

US President Donald Trump has signed directives to begin building a wall along the 3,200km US border with Mexico.

Trump says the proposed 1,600km border wall will make both the US and Mexico safer.

More than 1,000km of the US-Mexican border already has some kind of barrier. Natural obstacles line the other 1,600km.

Condemning the move, Mexican President Pena Nieto said that his country "will not pay for any wall", referring to Trump's campaign promise that Mexicans will pay for the wall.