The entire US-Mexico border wall will be painted black to make it hotter and harder to climb, Homeland Security Secretary Kristi Noem has said, crediting the idea to President 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.

Crossings and detentions of undocumented immigrants have plummeted since Trump returned to the office, with record lows of approximately 4,600 in July and 6,000 in June - a 92% year-on-year reduction.

During the Biden administration, detentions sometimes spiked to averages of 6,000 per day.

Earlier in August, Noem said that a total of 1.6m undocumented immigrants have left the US during the first 200 days of the Trump administration, although she did not specify how many have been deported and how many left on their own.

White House Press Secretary Karoline Leavitt said earlier in August that a total of 300,000 undocumented immigrants had been detained in the interior of the US since January.

While the administration continues to say it is prioritising those with criminal histories, immigration advocates have warned that many with no criminal charges or only minor infractions have been caught up in the sweeps.

White House officials also contend that increased border security and mass deportations have been deterrents, saying they are the primary reason for plummeting figures at the US-Mexico border.