White House chief of staff John Kelly, who is set to leave the Trump administration within days, flatly asserted in remarks published Sunday that the president's proposed border project "is not a wall" and that all plans for a concrete wall were abandoned long ago -- directly contradicting the White House's repeated claims.

In a series of Twitter posts earlier this month, Trump insisted that "we are not building a Concrete Wall, we are building artistically designed steel slats, so that you can easily see through it." But Kelly's comments were seemingly at odds with the president's tweet on Friday calling for "money to finish the Wall," as well as his promises during and after the 2016 presidential campaign.

The relationship between Trump and Kelly has reportedly deteriorated in recent months. Trump announced in early December that the retired four-star Marine general would soon "move on" despite previously suggesting he would remain in the post through 2020.

"To be honest, it’s not a wall,” Kelly said in an interview with The Los Angeles Times. “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."

Within hours, the White House pushed back on Kelly's comments by highlighting Trump's earlier tweets on the topic.

"I think many people who don't want to fess up to border security and get Congress to do its job and close the loopholes insist it's a wall, wall, wall," Trump adviser Kellyanne Conway told CNN Sunday. "The president has said, he said last week, and he tweeted out pictures of steel slats. Things are already happening in California in terms of that."

She added: "It really depends on what Customs and Border Patrol says they need. And they have said they need barriers. The president says a wall -- barriers, the president says they need steel slats. They need technological enhancements."

But, reacting to the news that a second migrant child died this month while in the custody of U.S. officials, Trump seemingly suggested that Border Patrol agents do, in fact, want a wall.

"To be honest, it’s not a wall." — Outgoing chief of staff John Kelly

"The father of the young girl said it was not their fault, he hadn’t given her water in days," Trump wrote. "Border Patrol needs the Wall and it will all end. They are working so hard & getting so little credit!"

And on Sunday, Trump said the U.S. needs a wall only "slightly larger" than the one surrounding what he called former President Obama's "D.C. mansion/compound."

The president also doubled down on his campaign pledge that Mexico would fund the wall -- and suggested in an earlier tweet that he had kept that promise.

"Mexico is paying (indirectly) for the Wall through the new USMCA, the replacement for NAFTA!" Trump wrote. "Far more money coming to the U.S. Because of the tremendous dangers at the Border, including large scale criminal and drug inflow, the United States Military will build the Wall!"

Jakelin Caal, 7, and 8-year-old Felipe Gomez Alonzo were each detained this month after entering the U.S. with their undocumented fathers. Jakelin suffered from dehydration and shock, while Felipe died just before 11:50 p.m. on Christmas Eve after falling ill with flu-like symptoms.

Felipe's father, Agustin Gomez, had seized “the opportunity” to travel to the Mexico border in hopes of migrating to the U.S. after hearing a rumor, according to Felipe’s stepsister, Catarina Gomez Lucas.

"We heard rumors that they could pass (into the United States). They said they could pass with the children," Lucas told the Associated Press.

Fox News has learned that behind the scenes this weekend, several senators are discussing a new potential compromise to end the ongoing partial federal government shutdown. One bipartisan proposal is to provide $5.7 billion in funding for the border wall, as well as a congressional reauthorization of the Obama-era Deferred Action for Childhood Arrivals (DACA) program for those brought to the U.S. illegally as children, along with some other immigration provisions.

There has also been talk about a special allowance for some classes of Central American refugees to be granted a more robust asylum status.

Speaking to CNN's "State of the Union" on Sunday, South Carolina Republican Sen. Lindsey Graham suggested that a compromise could be reached -- but only on one condition.

“To my Democratic friends: There will never be a deal without wall funding," Graham said.

Separately, Kelly told The Times that he made sure that, contrary to critics' claims, the president was always kept informed before making key decisions.

“It’s never been: The president just wants to make a decision based on no knowledge and ignorance,” Kelly told the paper. “You may not like his decision, but at least he was fully informed on the impact.”

Kelly pointed to one potential major lifestlye change in retirement, noting that he currently works from 4 a.m. to 9 p.m., and has limited freedom of movement.

“I’m guarded by the Secret Service. I can’t even go get a beer,” he joked.

Fox News' Chad Pergram contributed to this report.