crediting the idea to Donald Trump. While domestic detentions and deportations have been the primary focus of the current immigration crackdown, Trump's policy bill passed earlier this summer also allocated $46m (£34m) for additional wall construction. About a half mile (0.8km) of wall is going up each day along the nearly 2,000 mile (3,218km) border, according to Noem. The number of border crossings has plummeted in recent months, and the Trump administration says sweeping arrests and detentions are acting as a deterrent to illegal migration.

Speaking to reporters along a section of the border in New Mexico, Noem said on Tuesday that the black paint was "specifically at the request of the president". "[He] understands that in the hot temperatures down here, when something is painted black it gets even warmer and it will make it even harder for people to climb," she added. Border Patrol officials also say that black paint will help prevent the wall from rusting. Additionally, Noem said the administration is planning to install more "waterborne infrastructure" along the Rio Grande, which makes up more than half of the border between the two countries. While Noem did not provide any more details on those projects, Texas authorities have previously installed floating barriers - large orange buoys - and fortified riverbank fencing guarded by state troopers, local police officers and the Texas National Guard along parts of the river. (BBC)