The US-Mexico border wall will be painted black to make it hotter and more difficult to climb, Homeland Security Secretary Kristi Noem has announced, saying the directive came directly from Donald Trump.

Speaking to reporters in New Mexico on Tuesday, Noem said the decision to use black paint was "specifically at the request of the president".

She added: "[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." Border Patrol officials have also argued the coating will help protect the wall from rust.

The move comes alongside the Trump administration’s broader immigration crackdown, with detentions and deportations forming the core of its strategy.

While the focus has largely been on domestic arrests, Trump’s landmark spending bill passed earlier this summer also allocated $46 million for new wall construction.

Noem said around half a mile (0.8km) of wall is being built every day along the nearly 2,000-mile (3,218km) stretch of the border.

She also revealed that more "waterborne infrastructure" is planned along the Rio Grande, which makes up more than half of the border.

While she did not give further details, Texas authorities have previously installed floating barriers, riverbank fencing and deployed police, state troopers and the National Guard to patrol certain areas.

According to government data, border crossings and detentions have dropped sharply since Trump returned to office.

Only about 4,600 people were apprehended in July and 6,000 in June, a 92 percent reduction compared to last year. Under the Biden administration, detentions at times averaged 6,000 per day.

Noem also said earlier in August that 1.6 million undocumented immigrants have left the US in the first 200 days of Trump’s administration, though she did not specify how many left voluntarily and how many were deported.

Separately, White House Press Secretary Karoline Leavitt said about 300,000 undocumented immigrants have been detained within the US since January.

Officials maintain that enforcement efforts are focused on individuals with criminal histories, but immigrant advocates argue that many with no charges or only minor infractions have also been caught in the sweeps.

The White House has insisted that stricter border controls and large-scale removals are the main drivers behind the falling migration figures.