Acting Homeland Security chief Kevin McAleenan said separating migrant families at the U.S. southern border is "not on the table," and the policy was "not worth it" from an enforcement perspective.

In his first network interview as acting DHS secretary to broadcast, McAleenan told NBC News' Lester Holt on Tuesday, "We're not pursuing that approach."

McAleenan's predecessor, Kirstjen Nielsen, was forced out of the job earlier this month, in part because she'd refused to reinstate the policy of separating children from their families at the border, U.S. officials have told NBC News. Nielsen had implemented the policy last year, but it was blocked by the courts.

Asked if he thought the policy had been effective, McAleenan hedged.

"So prosecuting violations of the law does have a consequence and it does deter behavior. But it did not work if you lose the public trust," he said, adding that from an "enforcement perspective, it’s not worth it."

Of the children separated from their families at the border, McAleenan claimed "they were always intended to be reunited," which is a "part of this story that I think had been lost."

"But again we're not pursuing that approach," he continued in an interview from DHS's offices in the World Trade Center. "Really a better system, as I've said many times, would allow us to detain families together during fair and expeditious immigration proceedings and getting actual immigration results from courts, so that’s what’s missing from the current situation."

McAleenan insisted the family separation policy wasn't coming back.

"I think the president has been clear that family separation is not on the table and again this was a zero tolerance prosecution initiative that was targeted at adults violating the law. It did have the impact of several 2,000-plus families being separated during that prosecution," he said.

He said a judge’s order to reunite the families last year just sped up a process that was already in place.

"These processes were going to reunite parents and children after the prosecution, after the immigration proceeding, and really what the ... court order did is it mandated that happen more quickly," McAleenan said.

"And, really, it was done very effectively. Border patrol agents kept very careful records between the relationships between parents and children, and those connections were made very expeditiously by Health and Human Services working with the Department of Homeland Security," he said.

DHS’s acting inspector general John Kelly had a different take in a report he issued in October that found "DHS was not fully prepared to implement the administration's zero-tolerance policy or to deal with some of its after-effects." The report also found that Customs and Border Protection, which had been led by McAleenan, "lacked the ability to reliably track children separated from their parents, and in some cases failed to adequately inform parents about the separation policy."

In the interview, McAleenan also pushed back on reports by CNN and The New York Times that President Donald Trump had told him he should close the southern border and would pardon him if he faced any legal challenges.

"I'm not going to do anything that violates the law ever. I'm a law enforcement official," McAleenan said. "I've been asked to serve in this role, and I'll carry that out, with full focus on my legal duties. That said, I've never been asked, never been suggested to do, anything unlawful by the president or anyone else. And I wouldn't do it."

He acknowledged: "It's challenging when you have people filling in new roles."

"But the good thing about DHS is we've got a tremendous reservoir of career leadership, a lot of executive talent. These are folks that I've come up with through the ranks that I know very well. I know what their capabilities and qualities are," he said.

"Everybody's focused on keeping our momentum and making sure we carry out all of our various missions effectively."

Asked if he was concerned about the job's turnover rate — McAleenan is the fourth DHS secretary in Trump's two years in office — he said, "I'm getting tremendous support from the White House."

"I intend to keep that support by, by taking the steps we need to address the situations we're facing," he said.