The concrete border wall that President Trump has repeatedly called for as a signature campaign promise is not actually a wall and has not been since “early on in the administration,” the outgoing White House chief of staff, John F. Kelly, said in an interview published Sunday.

The comments further muddy the administration’s position as Mr. Trump demands that Democrats provide $5 billion in funding for a wall on the border with Mexico, an impasse that has led to a partial government shutdown after the president abruptly pulled out of a compromise deal to keep the government funded through February. They were also notable given Mr. Trump’s insistence for most of his term that the border would have a wall, not the “steel slat barrier” he has pivoted toward in the past few weeks.

“To be honest, it’s not a wall,” Mr. Kelly told The Los Angeles Times.

Mr. Kelly, whose last day in his role is Monday, said he had sought advice from Customs and Border Protection officials early in 2017, when he was the homeland security secretary. Mr. Kelly said he was told that “we need a physical barrier in certain places, we need technology across the board, and we need more people.”

He went on: “The president still says ‘wall’ — oftentimes frankly he’ll say ‘barrier’ or ‘fencing,’ now he’s tended toward steel slats. But we left a solid concrete wall early on in the administration, when we asked people what they needed and where they needed it.”