Not necessary to justify separating kids, parents at border, 'it's zero tolerance’: Bannon The former White House chief strategist said Trump is "enforcing the law."

Former White House Chief Strategist Steve Bannon said President Donald Trump doesn’t need to “justify” the policy of separating children from parents who are caught illegally crossing the southern U.S. border because the it is part of the administration's “zero tolerance” approach on illegal immigration.

“It’s zero tolerance. I don't think you have to justify it,” Bannon, who was also CEO of Trump's presidential campaign, said to ABC News Chief White House Correspondent Jonathan Karl in an exclusive interview on “This Week” Sunday.

“We ran on a policy -- very simply -- stop mass illegal immigration and limit legal immigration, get our sovereignty back to help our workers, and so he went to a zero tolerance policy," Bannon said. "It's a crime to come across illegally and children get separated. I mean, I hate to say it, that's the law and he's enforcing the law.”

Nearly 2,000 migrant children -- 1,995 -- were separated from 1,940 adults between April 19 and May 31, after being caught illegally crossing the border, a Department of Homeland Security official told reporters during a conference call Friday.

The separation policy follows Attorney General Jeff Sessions' announcement on April 6 of a “zero-tolerance” immigration policy that includes criminally prosecuting illegal border-crossers, thus separating them from children who under U.S. law cannot be held in criminal detention centers.

“If you cross this border unlawfully, then we will prosecute you. It’s that simple," Sessions told a conference of state criminal investigation agencies in Arizona in April. “If you are smuggling a child, then we will prosecute you and that child will be separated from you as required by law. If you don’t like that, then don’t smuggle children over our border.”

Karl asked Bannon on Sunday about the widespread criticism of the family separation policy, including from religious leaders such as top evangelical Franklin Graham, a Trump supporter, and Cardinal Timothy Dolan, the Catholic archbishop of New York.

Pope Francis posted a tweet last week that some interpreted as referring to the new U.S. practice of placing migrant children in centers separate from their parents.

“The pope more than anybody else has driven the migrant crisis in Europe,” Bannon responded, noting that he is himself a Catholic. “The Catholic Church is one of the worst instigators of this open-borders policy.”

Trump has repeatedly, falsely asserted that a law passed by Democrats is to blame for the family-separation policy. Just on Friday, an ABC News fact check found Trump repeated this false claim at least seven times.