Outgoing White House chief of staff John Kelly told the Los Angeles Times that President Donald Trump's long-promised addition to the southern US border won't actually be a wall.

Kelly's comments are the latest development in the Trump administration's changing rhetoric on the president's long-promised wall along the southern US border.

As the wall has come under scrutiny while at the center of gridlock in Congress, Trump has changed his description of his early campaign promise, saying it would be more like "fencing" that was an "artistically designed" set of steel slats, not concrete.

Outgoing White House chief of staff John Kelly said President Donald Trump has changed his plans for the structure he wants built along the US-Mexico border.

"To be honest, it's not a wall," Kelly told the Los Angeles Times in a wide-ranging interview.

Kelly said the solid concrete wall Trump had touted throughout his campaign and early administration was a past plan, and the president was embracing plans for other types of structures.

"The president still says 'wall' — oftentimes frankly he’ll say 'barrier' or 'fencing,' now he’s tended toward steel slats," Kelly told the Times. "But we left a solid concrete wall early on in the administration, when we asked people what they needed and where they needed it."

Read more: Most Americans would rather spend the $5 billion Trump is demanding for the border wall on infrastructure, education, or healthcare

Counselor to the president Kellyanne Conway echoed Kelly's comments later Sunday, calling outcry over the wall "a silly semantic argument."

"It is a silly semantic argument because people who just want to say 'wall, wall, wall' want it to be a four-letter word and not respect what Customs and Border Patrol tell us they need," Conway said on "Fox News Sunday."

She continued: "Always saying 'wall' or 'no wall' is being very disingenuous and turning a complete blind eye to what is a crisis at the border."

The Times noted that from his time heading Homeland Security in 2017, Kelly valued input from "people who actually secure the border," the Customs and Border Protection agents on the ground.

Kelly noted the agents said they needed a "physical barrier in certain places," in addition to "technology across the board," and "more people."

Trump had notably changed his tune as he grew increasingly volatile towards lawmakers who stood in the way of funding approval, saying it would be more like "fencing," that was an "artistically designed" set of steel slats, not concrete.

But Trump has continued to refer to his planned border structure as the "Wall." Saturday Trump tweeted that "If we had a Wall," it would have deterred migrant children who died in Customs and Border Protection custody from coming to the US at all.

The federal government is currently in a partial shutdown over gridlock in Congress that failed to approve Trump's demand for $5 billion dedicated to the wall's construction.

President Donald Trump announced earlier this month that Kelly would be leaving his role by the end of the year.